I only have enought for 2 games. Gears Of War 2, and Fallout 3, or fable 2.

Go with Fable 2, if you have Xbox-Live.
Go with Fallout 3 if you don't have Xbox-Live

I'd go with Fable 2.

Go with fable 2 it has a lot of innovative feature like having kids and owning a shop, don't get me wrong fallout 3 is going to be a great game but I think Fable 2 will satisfy me more in the long run.

Those 3 are the ones I'm thinking about too so this is what I did:

I postponed buying Fallout 3 because they always come out with the expansion pack with the game at cheaper prices. So I'm just going to buy Gears 2 and Fabe 2 which will keep you occupied for about a year until whatever Fallout 3 Gold Edition will come out.