Wii: Super Mario Galaxy. As soon as I saw videos for it I had to have it, and is now one of my favorite games of all time. And I was a 3D mario hater before it.

DS: New Super Mario Bros. I love 2D mario games :D

PS3: GTA IV. GTA is one of my favorite series, so I had to play it. Uncharted as well just because it looked amazing, and it is.

X360: I dont have a 360, but Alan Wake almost made me buy one, so that would be the system seller for me. I may still get one in the future once finances are in order.

Fallout 3 compelled me to purchase an Xbox 360 in late 2008. The price of a PS3 at that time was still around $600 for the "elite" and I believe $400 for the entry. My used Xbox 360 cost me $192.00 including shipping.

PS3: Blu ray (wanted to play my wedding blue ray footage), plus the games library, mainly MGS4, LBP and KZ2.

Don't own any other systems atm, though I'm starting to get tempted by handhelds.

Wii and DS: Bought them instantly for future Nintendo titles

PS3: Combination of games like Valkyria Chronicles and LBP and upcoming titles such as FF XIII and for Team ICO

Wii: LoZ: Twilight Princess

X360: Halo 3

PS3: Final Fantasy XIII

DS: Nintendogs

PSP: Lumines; Ridge Racer

I'll include the last generation of consoles:

GC: Luigi's Mansion; SWR: Rogue Squadron II

PS2: Final Fantasy X

Xbox: Halo 2

GBA: Animal Crossing (GameCube) Connectivity 

And just for fun my future System Sellers:

WiiToo: the next StarFox & F-Zero (if they don't get released for Wii)

X720: Halo (whatever name/number/genre it will have)

PS4: Final Fantasy XV or XVI (only if it's a regular non-MMORPG FF)

3DS: Nintendogs Cats (now with 3-D fur)

PSP2: Final Fantasy VII Remake (one can dream)

Wii: Mario Kart Wii

DS: New Super Mario Bros.

PS3: God of War III and Uncharted 2

Xbox360: Fable III, I'm sure it is that good (because I don't like that much shooters except of Half-Life)

He clearly said THIS gen, way to break the rules.

PS3: Valkyria Chronicles, LBP, the hope (at the time) that Deomn's Souls would get an EMEAA release which it did - Yay! Buzz Quiz TV, Singstar, PSOne classics on PSN.

If I buy a Wii one day, the only Nintendo game franchise that's really interested me is Zelda.

If I buy a 360 one day, Mass Effect is what interests me the most, Fable seems like an interesting franchise too.

Who knows when I'll get a PC capable of playing post 2007 games, probably in 2012 some time.

Advance Wars DS, Halo 3 and Super Mario Galaxy were the system sellers for me. With PS3 & PSP it was a combination of games.

Exactly that for me too, though both consoles have proven to have many console sellers as I've been proven lately.