You can run games like DOOM 3 which demand alot from your video card with no problems on a 128 MB vid card, Now aday video cards then to come out every other month when one manufacturer comes out with a new chip set its competitor comes out with a competing chip set. The bottom line is this if you want to run a current game out there right now that push your vid cards to the limits you do not need the most recent video card out there. If you get a decent (128 mb) video card you should be able to enjoy almost all the games out there even the newest ones on lower settings. If you are a hard core gamer I would recommend you go with a 256 Mb vid card other than that stick with a decent 128 Vid card. Shop around online for the best prices this it the one I use I got mine for 49 USD On ebay 

http://www.shopbot.com.au/p-10488.html

I can run all the games out there that I play Doom3, COD (when I feel like beating CON) WOW, and TANX :p