This list is totally incomplete because it's pretty hard to remember all the bands, especially all the unknown supporting bands. I also don't remember every concert I attended before 2004 because I didn't keep track back then. From 2005 on the list is almost complete. But I have to say I don't necessarily like all of the bands even if I saw them more than once - that just happens sometimes at festivals. This list includes only true musicians, I spare you the plastic pop shit bands I saw when I was a teenager (well that was in the 90's).
and yeeees I am addicted to live music and obsessed with live music - can't help it ;)

Top List:
Donots: 30 x
Mando Diao: 17 x
Beatsteaks: 14 x
Johnossi: 12 x
Itchy Poopzkid: 11 x
Placebo: 11 x
Sugarplum Fairy: 11 x
The Wohlstandskinder: 10 x
4Lyn: min. 9 x
Fettes Brot: min. 9 x
Bosse: 9 x
Die Ärzte: 9 x
Sportfreunde Stiller: 9 x
Mad Caddies: 8 x
Muff Potter: 8 x
Slut: 8 x
Turbostaat: 8 x

all bands in alphabetical order:
(hed) Planet Earth: 2 x (2001)
...And You Will Know Us by the Trail of Dead: 1 x (2007)
28 Days: 1 x (2001)
3 Doors Down: min. 4 x (2000/2001/2003/2006)
30 Seconds to Mars: 1 x (2007)
4Lyn: min. 9 x (4x2001/2x2002/2003/2x2006)
5 Bugs: 3 x (2004/2006/2008)
10 Years: 1 x (2006)
1000 robota: 2 x (2007/2008)
A: 1 x (2002)
Abwaerts: 1 x (2006)
A Camp: 1 x (2001)
A Chinese Restaurant: 1 x (2006)
a-ha: 1 x (2001)
Aiden: 2 x (2006)
Air: 2 x (2004/2007)
Alex Amsterdam: 2 x (2008)
Alexisonfire: 1 x (2006)
Alien Ant Farm: 1 x (2001)
Amplify: 3 x (2x2006/2008)
Amusement Parks on Fire: 1 x (2006)
Anna Ternheim: 1 x (2007)
Anti-Flag: 5 x (2002/2004/2006/2x2008)
Apartment: 1 x (2005)
Apoptygma Berzerk: 1 x (2008)
Archive: 4 x (3x2006/2007)
Arctic Monkeys: 4 x (2x2006/2x2007)
Art Brut: 1 x (2007)
As I Lay Dying: 1 x (2006)
Ash: 5 x (2001/2x2004/2x2007)
Richard Ashcroft: 2 x (2005/2006)
Audioslave: 1 x (2005)
auletta: 2 x (2008)
Babyshambles: 2 x (2006/2008)
Backyard Babies: 1 x (2001)
Bad Religion: 3 x (2x2000/2008)
Bat For Lashes: 1 x (2008)
Battle: 1 x (2006)
Beans on Toast: 1 x (2006)
Beatsteaks: min. 14 x (2x2001/2x2002/2003/2x2004/2005/4x2007/2x2008)
Beck: 1 x (2001)
Bedouin Soundclash: 1 x (2008)
Bernd Begemann: 1 x (2008)
Bela B.: 1 x (2006)
Bell-X1: 2 x (2003/2008)
Belvedere: 1 x (2004)
Biffy Clyro: 1 x (2008)
Billy Talent: 3 x (2006/2x2007)
Björn Dixgård: 1 x (2007)
Blackmail: 5 x (2001/2006/2007/2x2008)
Black Rebel Motorcycle Club: 2 x (2007/2008)
Black Rust: 1 x (2008)
Blind: 1 x (2007)
Blind Terry: 1 x (2008)
Blink-182: 1 x (2000)
Bloc Party: 1 x (2007)
Bloodhound Gang: 2 x (2000/2006)
Blood Red Shoes: 2 x (2007/2008)
Bloodsimple: 1 x (2006)
Blumfeld: 1 x (2001)
Bomb Texas: 1 x (2008)
Bondage Fairies: 1 x (2007)
Bosse: 9 x (4x2005/3x2006/2007/2008)
The Bouncing Souls: 1 x (2006)
Boy Hits Car: min. 1 x (2001)
boysetsfire: min. 1 x (2005)
Brainless Wankers: min. 1 x
British Sea Power: 1 x (2008)
Bubonix: 2 x (2008)
Buena Vista Social Club: 1 x (2008)
Bullet for My Valentine: 2 x (2006)
Caesars: 1 x (2003)
Calexico: 1 x (very short) (2008)
Cave In: 1 x (2003)
Cazals: 1 x (2008)
Chicago Jazzz: 2 x (2000/2001)
Chuck Ragan: 1 x (2007)
Clawfinger: 1 x (2001)
Colbie Caillat: 1 x (2007)
Cold War Kids: 2 x (2007)
Coldplay: 1 x (2005)
Cosmotron: 1 x (2002)
Crazy Town: 1 x
Crosscut: 1 x (2001)
Culcha Candela: 2 x (2005/2008)
Dag för Dag: 1 x (2008)
Daniel Cirera: 1 x (2007)
Danko Jones: 3 x (2004/2006)
Dan Sartain: 1 x (2008)
David Bowie: 1 x (2004)
David Huhn Band: 1 x (2007)
David Kitt: 1 x (2002)
David & the Citizens: 1 x (2006)
Dawn Penn: 1 x (2004)
Days in Grief: 1 x (2005)
December Peals: 1 x (2006)
Deftones: 3 x (2000/2001/2006)
Dega Brakes: 1 x (2006)
Heideroosjes: 1 x (2001)
Depeche Mode: 1 x (2006)
derrick brown: 1 x (2007)
Destiny on Holiday: 1 x (2006)
dEUS: 1 x (2006)
Dew-Scented: 1 x (2007)
Diamond Nights: 2 x (2005)
Die Ärzte: 9 x (2000/3x2001/2002/2005/2006/2007/2008)
Die Fantastischen Vier: 3 x (2000/2004/2007)
Die Happy: 3 x (2001/2004/2007)
Die Raketen: 1 x (2004)
Die Sterne: 2 x (?/2006)
Die Toten Ärzte: 1 x (2007)
Die Toten Hosen: 3 x (2004/2x2008)
Dioramic: 1 x (2008)
Dirty Pretty Things: 2 x (2007)
Disco Ensemble: 7 x (2x2006/2x2007/3x2008)
Does It Offend You Yeah?: 1 x (2008)
Dog Eared Pages: 1 x (2008)
Dog Eat Dog: min. 1 x (2006)
Donavon Frankenreiter: 1 x (2006)
Donots: 30 x (2000/6x2001/2x2002/6x2004/2x2005/4x2006/4x2007/6x2008)
Downride: 1 x (2006)
dredg: 2 x (2002/2006)
Dressed: 1 x
Dropkick Murphys: 2 x (2004/2006)
Dúné: 2 x (2008)
Eagles of Death Metal: 1 x (2007)
Echt: min. 5 x (1998/1999)
Eight Legs: 1 x (2008)
Elbow: 1 x (2006)
Elefant: 1 x (2004)
Elefants: 1 x (2008)
EL*KE: 1 x (2007)
Emil Bulls: min. 1 x (2001)
Enter Shikari: 2 x (2007/2008)
Escapado: 1 x (2008)
Eskobar: 1 x (2008)
Evanescence: 1 x (2007)
exits to freeways: 1 x (2008)
Eyesight: 1 x (2007)
Fabo: 1 x (2006)
Falco Solo: 1 x (2008)
Farin Urlaub: 1 x (2006)
Feeder: 1 x (2001)
Felix da Housecat: 1 x (2004)
Fettes Brot: min. 9 x (1998/1999/2x2000/2002/2006/3x2008)
Finley: 1 x
Fire in the Attic: 2 x (2006/2008)
Five Fast Hits: 1 x (2006)
Flipsyde: 1 x (2006)
Flogging Molly: 3 x (2x2005/2008)
Foo Fighters: 4 x (2000/2001/2006/2008)
Fotos: 3 x (2007/2x2008)
Frank Black: 1 x (2007)
frank spilker gruppe: 1 x (2008)
Franky Lee: 1 x (2006)
Franz Ferdinand: 1 x (2006)
Fräulein Wunder: 1 x (2008)
Freitag: 1 x (2002)
Freunde der Nacht / Ruhe (Nagel): 2 x (2006/2008)
From Autumn to Ashes: 1 x (2007)
FUZZY CASINO: 1 x (2007)
GARLIC BOYS: 1 x (2001)
Gary: 2 x (2000/2001)
GEM: 1 x (2006)
Gentleman & The Far East Band: 2 x (2004/2005)
Gimcrack: 1 x (2000)
Gisbert zu Knyphausen: 1 x (2008)
Godsmack: 1 x (2001)
Gods of Blitz: 2 x (2007)
Goldfrapp: 1 x (2006)
Good Charlotte: 1 x (2007)
Good Shoes: 1 x (2007)
Green Day: 1 x (2001)
Guano Apes: 2 x (2000/2001)
Guns N' Roses: 1 x (2006)
H-Blockx: min. 3 x (2001/2002/2005)
Hard-Fi: 1 x (2006)
Hallo Kwitten: 1 x (2007)
Havana Heat Club: 1 x
Helicopter: 1 x (2007)
Hellogoodbye: 1 x (2006)
Hero: 1 x (2008)
Herrenmagazin: 1 x (2005)
Herzer: 1 x (2002)
H.I.M.: 2 x (2001)
HOO DOO GIRL: 1 x (2008)
Honeyheads: 1 x (2008)
Hosh: 1 x (2001)
Hot Chip: 1 x (2008)
Hot Hot Heat: 1 x (2007)
Howling Bells: 2 x (2006)
HushPuppies: 2 x (2006/2008)
Ian O'Brien-Docker: 1 x (2007)
Ignite: 1 x (2001)
Ill Niño: 2 x (2002)
Incubus: 2 x (2006/2008)
Interpol: 1 x (2007)
Itchy Poopzkid: 11 x (2005/4x2006/6x2007)
Ja, Panik: 1 x (2008)
Jamie T.: 1 x (2007)
Jamiroquai: 1 x (2006)
Jet: 2 x (2007)
Jimmy Eat World: 5 x (2001/2004/2005/2x2008)
Jim Pansen: 1 x (2008)
Jingo De Lunch: 1 x (2007)
JJ72: 1 x (2001)
Jonathan Wilkes: 1 x (2006)
Johnny Foreigner: 1 x (2008)
Johnossi: 12 x (4x2006/5x2007/3x2008)
Julia: 1 x (2006)
Juliette & The Licks: 2 x (2007)
Justice: 1 x (2008)
Justin Balk: 1 x (2006)
Kain: 2 x (2006)
Kaiser Chiefs: 4 x (2006/2x2007/2008)
Kaizers Orchestra: 1 x (2006)
kapaikos: 1 x (2008)
Kapelle Petra: 2 x (2005)
Karamel: 1 x (2008)
Karpatenhund: 2 x (2005/2007)
Kate Nash: 1 x (2008)
Keane: 1 x (2005)
Kettcar: 4 x (2001/2x2005/2008)
Kid Rock: 2 x (2001/2008)
Kilians: 2 x (2007)
Kill the Young: 1 x (2008)
Kim Frank & Band: 1 x (2007)
kontainer: 1 x (2008)
KoЯn: 2 x (2006/2007)
Krezip: 3 x (2001/2x2006)
Krieger: 1 x (2006)
Kristeen Young: 1 x (2006)
Kungfu: 1 x (2002)
Ladytron: 1 x (2006)
Lagwagon: 1 x (2006)
Lapko: 2 x (2007/2008)
Last Sunday: 1 x (2006)
Laura Imbruglia: 1 x (2008)
La Vela Puerca: 1 x (2005)
leo can dive: 2 x (2007)
Less Than Jake: 3 x (2001/2006/2007)
Lifehouse: 1 x (2001)
Limp Bizkit: 1 x (2000)
Linkin Park: 2 x (2001)
Little Man Tate: 1 x (2007)
Long Distance Calling: 1 x (2008)
Lostprophets: 2 x (2002/2008)
Lotto King Karl: min. 1 x (1996)
Louis 14: 1 x (2006)
Loui Vetton: 2 x (2008)
Lovebugs: 2 x (1997)
Lukas Kasha: 1 x (2007)
Machine Head: 1 x (2007)
Mad Caddies: 8 x (2001/2004/2x2006/2x2007/2x2008)
Madsen: 6 x (2006/2x2007/3x2008)
Mando Diao: 17 x (2x2005/6x2006/7x2007/2x2008)
Manic Street Preachers: 5 x (3x2001/2007/2008)
Manu Chao: 1 x (2006)
Marathon: 1 x (2008)
Mark Owen: 6 x (2x1997/4x2005)
Marilyn Manson: 2 x (2007)
Maritime: 1 x (2004)
Matthew Jay: 1 x (2001)
Matula: 1 x (2008)
Maximo Park: 2 x (2006/2007)
Megadeth: 1 x (2007)
Metallica: 2 x (2006/2008)
Millencolin: 5 x (2000/2002/2x2005/2008)
MIA.: 1 x (2007)
MIR: 1 x
Mogwai: 1 x (2007)
Modest Mouse: 1 x (2007)
Molotov Jive: 7 x (2007)
Moneybrother: 1 (2008)
Monkey Wrench: 1 x
Montreal: 1 x (2007)
Alanis Morissette: 1 x (2001)
Morrissey: 2 x (2006)
Motörhead: 1 x (2008)
mr. marple: 1 x (2008)
Mudvayne: 1 x (2001)
Muff Potter: 8 x (2006/5x2007/2x2008)
Muse: 4 x (2000/2003/2006/2007)
My Baby wants to eat your pussy: 2 x (2007)
Myballoon: min. 1 x
Mystery Jets: 1 x (2006)
Nada Surf: 4 x (2008)
Negative For Francis: 1 x (2006)
Neil Young: 1 x (2008)
Neimo: 2 x (2008)
Nelly Furtado: 1 x (2001)
Neulich: 1 x (2001)
New Model Army: 1 x (2001)
Nickelback: 1 x
Jon Nicholson: 1 x (2006)
Nicht ohne meine Schwester: 1 x (2001)
nice boy music: 1 x (2006)
Nine Inch Nails: 1 x (2005)
N.M.E. Mine: 1 x (2006)
No Doubt: 1 x (2000)
NOFX: 2 x (2007/2008)
Noisettes: 1 x (2006)
No Mayers 50: 1 x (2006)
Oasis: 1 x (2005)
Ohrenfeindt: 1 x (2007)
Olli Schulz: 1 x (2007)
One Fine Day: 4 x (3x2006/2007)
OPM: 1 x (2001)
P:LOT: 1 x (2006)
Pale: 1 x (2002)
Panic at the Disco: 1 x (2008)
Pantéon Rococó: 2 x (2006/2008)
Paolo Nutini: 1 x (2007)
Papa Roach: 3 x (2001)
Paramore: 1 x (2007)
Parasiten: 1 x (2006)
The Peacocks: 2 x (2004/2007)
Pearl Jam: 1 x (2007)
Pennywise: 2 x (2006/2008)
Pete Blume: 3 x (2000/2x2006)
Pete Murray: 1 x (2008)
peters.: 1 x (2007)
PinBoys: 2 x (2006)
The Pink Mountaintops: 1 x (2007)
Placebo: 11 x (2000/2x2003/2x2004/5x2006/2007)
Please.me: 1 x (2008)
P.O.D.: min. 2 x (2002/2003)
Pohlmann: 4 x (3x2006/2007)
Polarstern: 1 x (2001)
Porcupine Tree: 1 x (2007)
Portugal. The Man: 1 x (2008)
Post Scriptum: 1 x (2008)
Powderfinger: 1 x (2001)
Queens of the Stone Age: 5 x (2001/2002/2005/2007/2008)
Racoon: 1 x (2008)
Radiohead: 1 x (2001)
Reamonn: 2 x (2000/2001)
Rafael Weber: 2 x (2007)
Rage: 1 x
Rage Against the Machine: 2 x (2008)
Raining Pleasure: 1 x (2007)
Rammstein: 2 x (2001/2005)
Randy: 1 x (2005)
Ransom: 1 x (2002)
Rantanplan: 2 x (2001/2004)
Razorlight: 4 x (3x2006/2008)
Readymade: 1 x (2002)
Recycled: 1 x (2002)
Red Hot Chili Peppers: 1 x (2002)
Reimzig: 2 x (2000/2008)
R.E.M.: 2 x (2005/2008)
Rhaatid feat. D-Flame + Metaphysics + Nneka: 1 x (2007)
Rhesus: 1 x (2007)
Rise Against: 1 x (2008)
Rising Down: min. 2 x
Rival Schools: 1 x (2008)
River City High: 1 x (2002)
Robbie Williams: 5 x (1997/1998/1999/2001/2006)
Roh: min. 1 x (1996)
Roman Fischer: 1 x (2008)
Rufus Wainwright: 1 x (2005)
Saosin: 1 x (2006)
Sarcevic, Nikola: 1 x (2006)
Satans fette Beute: 1 x (2007)
Satellite Party: 1 x (2007)
Schneller Autos Organisation: 1 x (2008)
Schrottgrenze: 3 x (2004/2x2006)
Second Monday: 1 x (2007)
Secret Machines: 2 x (2006)
Senses Fail: 1 x
Serj Tankian: 1 x (2008)
Serum 114: 1 x (2008)
Short Fuse Burning: 1 x (2007)
Shout Out Louds: 3 x (2006/2007/2008)
Siamoon: 1 x (2001)
Sibling Sense: 1 x (2008)
Sigur Rós: 1 x (2006)
Silverchair: 1 x (2003)
siva.: 1 x (2008)
Ska-P: 1 x (2005)
Skatoons: 1 x (2004)
Skin: 2 x (2006)
Slut: min. 8 x (2x2001/2x2005/2006/3x2008)
Snow Patrol: 1 x (2007)
Söhne Mannheims: 1 x (2008)
Sonic Youth: 1 x (2007)
Soulfly: 3 x (2002/2006/2007)
Spandau: 2 x (2004/?)
Sparkadia: 1 x (2008)
Sparta: 1 x (2007)
Spitting Off Tall Buildings: 1 x (2004)
Spittin Vicars: 1 x (2005)
Spooks: 1 x (2001)
Sport: 1 x (2008)
Sportfreunde Stiller: 9 x (2000/2001/2002/2004/2006/2007/2x2008)
Sprottenrock: 1 x (2007)
Spruce: 1 x (2007)
SR-71: 1 x (2001)
Staind: 1 x (2001)
Starsailor: 5 x (2x2001/2002/2003/2005)
Stars Play Music: 1 x (2008)
State Radio: 1 x (2008)
Stereophonics: 4 x (2005/3x2008)
Stone Temple Pilots: 1 x (2001)
Strapping Young Lad: 1 x (2006)
Strike Anywhere: 1 x (2004)
Sub7even: 1 x (2001)
Substyle: 1 x (2002)
Such a Surge: 2 x (2002)
Sugarplum Fairy: 11 x (6x2006/4x2007/1x2008)
Sum 41: 1 x (2007)
Sunrise Avenue: 1 x (2007)
The Supernaturals: 1 x (1997)
Superpunk: 1 x (2008)
Swosh!: 1 x (2004)
System of a Down: 2 x (2005/?)
Taking Back Sunday: 4 x (2004/3x2006)
Talk Radio Talk: 1 x (2008)
Taproot: 1 x (2001)
TempEau: 3 x (2x2006/2007)
The (International) Noise Conspiracy: 6 x (2001/2002/2004/2x2007/2008)
The 69 Eyes: 1 x (2007)
The Animal Five: 2 x (2007)
The Ataris: 1 x (2001)
The Audience: 1 x (2007)
The Bates: 1 x (1998)
The Blood Arm: 1 x (2007)
The Blue Van: 1 x (2007)
The Bravery: 1 x (2007)
The Cardigans: 1 x (2006)
The Chemical Brothers: 1 x (2008)
The Cinematics: 1 x (2008)
The Coast: 1 x (2008)
The Coral: 1 x (2007)
The Creetins: 1 x (2006)
The Cribs: 3 x (2x2007/2008)
The Darkness: 1 x (2006)
The Datsuns: 1 x (2007)
The Draft: 1 x (2007)
The Feeling: 3 x (2006)
The Films: 4 x (2006/3x2007)
The Fratellis: 2 x (2006/2008)
The Hives: 3 x (2006/2x2007)
The Jessica Fletchers: 1 x (2008)
The Killers: 1 x (2005)
The Kooks: 3 x (2x2006/2007)
The Mission: 1 x
The Pigeon Detectives: 1 x (2007)
Pixies: 1 x (2004)
The Prodigy: 1 x (2008)
The Raconteurs: 1 x (2006)
The Rain: 1 x (2007)
The Rakes: 1 x (2007)
The Ricky Kings: 1 x (2008)
The Rifles: 1 x (2006)
The Sea: 1 x (2008)
The Smashing Pumpkins: 1 x (2007)
The Sounds: 2 x (2007)
The Splash: 1 x (2001)
The Streets: 1 x (2008)
The Strokes: 1 x (2006)
The Subways: 2 x (2008)
The Thirst: 1 x (2007)
The Thrills: 1 x (2005)
The Ting Tings: 1 x (2008)
The Used: 2 x (2005/2007)
The Vandals: 1 x (2001)
The Verve: 1 x (2008)
The Weakerthans: 1 x (2008)
The White Stripes: 1 x (2007)
The Wohlstandskinder: 10 x (2002/3x2004/6x2005)
The Wombats: 1 x (2008)
Therapy?: 1 x (2001)
This is a Standoff: 1 x (2007)
This Familiar Smile: 1 x (2007)
Thomas D: 1 x (2001)
Those Dancing Days: 1 x (2008)
Three Chord Society: 1 x (2008)
Thumb: min. 2 x (2001)
Tocotronic: 1 x (2000)
Tokyo Police Club: 1 x (2008)
ton: 3 x (2006/2x2008)
Tool: 3 x (2001/2006/2007)
Toploader: 1 x (2001)
Trashmonkeys: 1 x (2005)
Travis: 3 x (2001/2x2007)
Tribute to Nothing: 1 x (2007)
Turbonegro: 4 x (?/2005/2006/2007)
Turbostaat: 8 x (5x2007/3x2008)
Underground Railroad: 1 x (2008)
Underoath: 1 x (2006)
Underwater Circus: 2 x (2001/?)
Virginia Jetzt!: 2 x (2007)
Walking Concert: 1 x (2004)
Walter Schreifels: 1 x (2008)
Waterdown: 3 x (2001/2x2006)
We Are Scientists: 1 x (2008)
White Rose Movement: 1 x (2006)
WideNoise: 1 x (2006)
Wil Ridge: 1 x (2008)
Wire Daisies: 1 x (2005)
Wir sind Helden: 3 x (2005/2006/2007)
WIZO: 1 x (2005)
Wolfmother: 1 x (2007)
Yellowcard: 1 x (2006)
Zed: 1 x (2004)
Zoo in a box: 1 x (2007)
Zoo TV: 2 x (2001/2008)
Zoot Woman: 1 x (2007)
ZOX: 1 x (2008)
ZSK: 1 x (2005)

and many many I forgot!

to be continued... (last update: 12.10.2008)