Would be good to know computer specs like how much MHz, RAM you have, and what is your price ceiling for my suggestion. Some of the best cost $200 and up. Assume you want to have better graphics for newer type games.
Here is a list, scroll down to the end of page on how they compare with different games.
http://www6.tomshardware.com/graphic/20031229/index.html
For prices, check newegg, scroll down to the end of page for clicking on the different Nvidia cards.
http://www.newegg.com/app/manufactory.asp?catalog=48&DEPA=1
I have a GeForce 4 TI 4600 on my WinXP, Pent 4, 2.0 MHZ, 512MB RAM desktop that plays the latest video games pretty good with no problems.
right now I'm running an nvidia 64 meg 400mx/mx
looking to upgrade it same brand or equivalent 128 meg
any sugestions?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic