These are the actual bands I've paid to see off the top of my head (missing at least another 100 I'd say when missing repeat gigs)...
AC/DC
Alexisonfire
Anthrax
Arch Enemy
Avenged Sevenfold
Black Label Society
Bad Religion
Blink 182
Chimaira
City and Colour
COG
Daft Punk
Danzig
Dark Tranquillity
Deftones
Dream Theater
Eric Clapton
Eric Johnston
Faith No More
Fantomas
Fear Factory
Frenzal Rhomb
Gamma Ray
Helloween
Incubus
In Flames
Iron Maiden
Joe Petrucci
Joe Satriani
Karnivool
Lamb of God
Lost Prophets
Machinehead
Megadeth
Metallica
Nightwish
The Misfits
Muse
Pearl Jam
Pennywise
Portishead
Queensryche
Offspring
Rammstein
RATM
Rise Against
Sepultura
Sevendust
Snob Scrilla
Sonata Arctica
Soulfly
Steve Vai
Static X
System of a down
Tomahawk
Then there is 8 BDO's, 4 soundwaves, 3 field days, 2 park lifes, 2 future music festivals, a come together festival, harvest festival, stereosonic, about 10 north american festivals (coachella, sonic boom x 2, heavy mtl x 2, lollapalooza and a few smaller ones)
Wow, you don't realise how many bands you've seen until you write it out, probably explains my bank balance... Best I've seen are City and Colour, Eric Clapton and Rise Against. Cog always hold a special place in my heart too.