A power supply model would be appreciated. Otherwise here are your two best betshttp://www.newegg.com/Product/Product.aspx?Item=N82E16814121426
GT440 1GB GDDR5 (will be more than enough for all games at low settings and 1280x720)http://www.newegg.com/Product/Product.aspx?Item=N82E16814102917
HD5670 1GB DDR5 (also good enough for new games with low graphics and 1280x720)
BUT For your system I would recommend something along the lines of these two cardshttp://www.newegg.com/Product/Product.aspx?Item=N82E16814130679
GTS450 1GB GDDR5 ( A true gaming graphics card, capable of maxing most games out with your resolution.)http://www.newegg.com/Product/Product.aspx?Item=N82E16814102898
HD5770 1GB GGDR5 (also a trooper that will max most games out with that resolution.)
Both of the cards I recommend ar the same price and perform very similar. HD5770 is above with maybe about 5%. But for future reference I recommend the GTS450 since nVidia tend to be more popular among game developers.