I know force is a little strong but what game will pursade you to just instantly buy a console or upgrade your PC to play it? 

For me Saints Row was the one that got me to buy a 360

For the Wii it will be Mario Kart

For the PS3 I currently don't have one but may end up getting on for the holidays as  blue-ray player.

For the PC currently all the games I would want are being made the 360 or PS3 including the mmo champions which is the next PC game that I would probably get.

 Of course this could change especially for the PS3 and PC since I am sure there will be more announcements of new games or current games announced that may surprise me.   

For me, Call of Duty 2 lured me to buy a 360.

Making $$$ was the reason I bought a Wii.

Reviewing games was the reason I bought a PS3.

I'd update my PC for Diablo 3 if it's ever release

Upgrade: StarCraft 2 + HL EP3 + Total War + (Lots of time with Indigo)
Consoles just for one game, nah, maybe 4...

Final Fantasy XIII may lure me into getting a PS3 next year. And my PC just needs some upgrading in general, sparkly new Graphics cards are out, so I'll get around to that eventually.

MGS4 for PS3

mario kart, ssbb, zelda, counter strike 3

I originally thought that FFXIII would make me buy a PS3 but now that I think about it, I'll probably just rent or borrow the system + game for a week or two and power through it.

Save many hundred bucks...

Back in the days Lord of the ring : The two towers got me on the PS2, I was mainly just gaming on the PC before ( MMO take so much time it was keeping me busy enough). But what can I say, I am ahuge LOTR fan...

Dang ... if we are going old skool ...

Atari 2600 - Combat
NES - Double Dribble
SNES - NCAA Basketball
Sega Genesis - Joe Montana Football
PS1 - RIDGE RACER
Xbox - Halo
PS2 - GTA3
Game Gear - Sonic the Hedgehog
N64 - Goldeneye FTW