My list (given i've been to a festival or two) is rather lengthy. And shane, you've missed out on the rolling stones.
Muse
The Smashing Pumpkins
Queens of the stone age (twice)
RHCP (twice)
Metallica
Slipknot (in support of the above)
Radiohead (twice)
God is an astronaut (4 times)
The Doves
Kasabian
The Kaiser Chiefs
Bloc party
The Prodigy
Ian brown
Laurent Garnier
MuM
Sigur Ros
The Saw Doctors (not proud)
Interpol
Green Day
Blink-182 (also not proud)
Mortiis
The Foo's
Nine Inch Nails
Tenacious D
Nas
The Flogging Molly
Death From Above 1979
The Streets (twice)
The Killers
Keane
Coldplay
The Rolling Stones
The Charlatans (twice)
Audioslave
Milo
LCD Soundsystem
Combichrist
The Arcade Fire
And i'm sure theres one or two more i'm missing. Now, on to what i wanna go see.
Hybrid
Unkle
Exodus
Kyuss *not ever going to happen*
Pink Floyd *as above*
Bruce Springsteen
Pearl Jam
Rage
Immortal Technique
Jedi mind tricks