Just don't go lower then a x4xx card, geforce 9400 for example. That is if you're a casual gamer. For more enjoyment (smooth gameplay, good quality) I'd suggest 9600 or better. Do your homework and do a little research on which card to get. Ask some questions on forums with people who have some hands-on experience. Those cards are expensive and it sucks to realize you made the wrong choice afterwards.
Good luck.
