I HAD to buy an XBox after my friends and I started playing multiplayer Halo. Since then (within a matter of weeks), between the 9 of us that play, we have 7 Xboxes (we have 3 networked in one house and 2 in another). Maybe it's just my group of friends, but I've never witnessed first hand a game sell so many systems. I absolutely had no interest in XBox until I got into multiplayer Halo. I even played the campaign mode a couple of times and wondered why people were so into it.
Street Fighter II Turbo made me buy an import and converter for my SNES, but that's the closest thing next to Halo.
Tekken Tag - PS2
Mario 64 - N64
Super Mario Bros. - NES
Castlevania: SOTN - GBA
And all have had many, many great games since
EDITED TO ADD: Now, with the XBox bundle, and Halo at $30 new, the temptation to pick one up is almost impossible...$230 for one game...
NES - Mario Bros.
SNES - Super Mario World
N64 - Super Mario 64
(see a pattern? )
GENESIS - Sonic the Hedgehog
SEGACD (I know... I know) - Sonic CD (best...sidescroller... ever)
GAMECUBE - Rogue Leader (or Super Mario Sunshine)
XBOX - HALO HALO HALO (Best Multiplayer console game... ever )
Well, I'm really glad that a bunch of other games I like came out for it (notably Eternal Darkness), but I bought my Cube specifically to play Resident Evil and its ilk. No ifs, ands, or buts. I go where my zombies go and will continue to do so.
If I had the disposable income I'd have a PS2 for GTA and Vice City alone. Not much else on the system has turned my crank that isn't available elsewhere.
Apple ][e Wizardry 1 Nintendo 64 Zelda. Still only have 2 64 games:b Playstation 2 GT3: A spec
The multitude of PC iterations, Playstation, Nintendo, xbox, dreamcast have no definate tie. Well, each PC upgrade can basically be tied directly to a new Ultima/Wing commander/Origin Systems game release if you want to nit.
Almost every system I've bought for at least 2 games, with the sole exception of the perhaps the N64.
Genesis - Sonic and EA's NHL games
TurboGrafx - Got a used one for $20 well after it had died so that I could play Galaga 90 and Alien Crush
Saturn - Virtua Fighter and Daytona
Playstation - Formula 1 and Resident Evil. Got WipeoutXL pretty damn quickly too.
N64 - Mario. Bought Pilotwings on launch day also. Didn't buy another until Zelda... a year after the game was released.
Gamecube - Mainly to play upcoming games (Mario, Starfox, Zelda) but I got it when I did cause I had to play Tony Hawk 3 and couldn't wait for the PC version.
The rest of the systems weren't really bought for any specific game.
This little bouncing block made my parents buy Pong.
Air Sea Battle made my parents buy Atari.
Castle Wolfenstein made my parents buy an Apple II+.
Shadow of the Beast made me buy an Amiga 500.
Hired Guns made me buy an Amiga 3000.
Todds Aventures in Slime World made me buy a Lynx.
Crash-n-Burn made me buy a 3DO.
Wipeout made me buy a PSOne.
Quake II made me buy a PC.
Resident Evil Veronica made me buy a DreamCast.
SSX made me buy a PS2.
Halo made me buy an Xbox.
My parents were happy when I could finally start affording my own stuff.
Sony Playstation- Resident Evil 2. I played a portion of it at my cousin's home in Denver and that is why I'm now a certified RE junkie. Heck, I even own RE: Survivor...
Sega Saturn- Daytona USA. Actually I'll have to include Virtua Fighter 2 and Virtua Cop since they were part of a limited-time offer were you got three free games when you bought a Saturn.
Sega Dreamcast- Resident Evil: Code Veronica. Like I said, I'm a junkie.
Nintendo Gamecube- Resident Evil. Didn't see that one coming.
Sony Playstation 2- I don't really own it yet, but I'm picking it up for Silent Hill 2.
Sega Genesis: Ghouls and Ghosts. Arcade-perfect.
SNES: Street Fighter 2 - I'm sure many others did this back in the day.
Nintendo 64: Mario 64 - the game that was really different at the time. Too bad the game caused every franchise to go 3D, many with bad execution.
Playstation: Final Fantasy VII. Saw the TV commercial in Japan. Friend showed me his copy from Japan. Sold. Bought the next day. i still consider it the last good Final Fantasy.
Playstation 2: Final Fantasy X, Metal Gear Solid 2. Both were good, but didn't have the same greatness as when I bought the PSX.