You have an integrated video solution where every videocard would give a performance gain. Quite cheap and powerfull are Ati 3800 series if they get thrown out cheap or Ati 4650-4670 series which is slightly slower but does not even need a powerconnector, so needs very few energy. On the NVidia site everything from 8600gt or 9000 series will easily do and they probably will be in your price range, too.
Edit: DO NOT GET A 7950 Card, this is two generations old and you will get a faster newer card for the same price or way cheaper!
Edit2: King of Kings solution is quite nice for a cheap and quite good card, this one would be way more powerful (i consider it an extremely good offer for its price), just costs 1.5:
http://www.newegg.com/Product/Produc...82E16814130401
Good Ati Cards:
http://www.newegg.com/Product/Produc...82E16814102792
http://www.newegg.com/Product/Produc...82E16814127384
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