I recently purchased an ATI graphics card, the HD5770..
This card has 1Gb of DDR5 Memory, an engine&shader clock of 850MHz (mid-range).
This card can be used in crossfire with up to 3 other ATI graphics cards (Quad-Crossfire). One of the great benefits of ATI crossfire is the ability to use different cards in crossfire and still experience a performace boost. Even a smaller compatable card will improve your gaming performance!
I play most of my games at >40fps on a resolution of 1900×1080.
Cod4 : 70-85fps on 1900×1080
GTA4 : 50-60fps on 1400×1024
Nfs undercover : 50-60fps on 1400×1024
I am very happy with the performance of this card, other than occasional lags on GTA4 i have no issues with it. Very happy!
I will get a second HD5770 and test the performance boost when crossfire is configured succesfully!