PS3 - 7 (Guitar Hero 3 & 4, Metal Gear 4, Stranglehold, Little Big Planet, Rock Band)
Xbox360 - 4 (Halo 3, Lego Indy, Kung Fu Panda (came with a controller) Fable 2)
Wii - about 20ish (shedloads of rubbish that never gets played except when friends are around)
PS2 - 2 (SSX Tricky, Metal Gear 2)
Xbox - 1 (SSX 3)
GameCube - 3 (Rogue Squadron, Resident Evil Remake, Fifa something or other (came with the unit))
DreamCast - 6 (Crazy Taxi, Resident Evil Code Veronica, Soul Calibur, Dead or Alive, Chu Chu Rocket, Jet Set Radio)
Playstation - 5 (Resident Evil Directors Cut, Resident Evil 2, Resident Evil Nemesis, Syphon Filter, Parasite Eve 2)
N64 - about 12
Jaguar 64 - maybe 4-5
3D0 - 2 Space Marines (as in the Games Workshop variety) and can't recall the name of the other.
Saturn - 1 (Virtual Cop w/ gun)
Mega 32x - Doom and Slipheed (was it?)
Mega CD - Night Trap
Megadrive (Genesis to you foreigners) - something like 15
Snes - about 12
Master System - 10
NES - 12 including the first two Zeldas and three Marios.
Atari 2600 - 14
I'm not listing all these for bragging rights - just I have them all wired up at home (PS3, Wii and both 360's are wired into my main TV (along with a HTPC with an AMD 3870 gfx card for games which we arbitrarily aren't mentioning for some reason) whilst everything else is set-up in my extension wired into a nice old CRT to give it that rustic feel).
Should really play them more as you can see I can barely recall the games I've got - currently my mountain bike sits in front of the TV in the extension - what does that say for my nerdiness

)
My main PC also has an AMD 4850 and a 22" screen which I use for gaming too.
[edit]
Should mention I'm more of a renter when it comes to games, especially the older consoles as a kid I couldn't afford to buy but pocket money covered the weekends rental and then I got a job in a video store so had carte blanch choice
[edit2]
Sorry - forgot I had rock band on the PS3 - chuffing annoying it doesn't support GH4's drums like the 360 version does.