I have an XFX Radeon HD 4850, it was kind of a budget card, but I'm impressed with it for the price. I can run GTA IV on Highest settings besides shadows, which are on high. It runs at 60-70 fps very well. It rarely ever drops to 40 fps, which is only when I have like 10 police cars behind me shooting me like crazy.
I can run Crysis on high at 40-50 FPS, Fallout 3 on Ultra at 80 fps and Just Cause 2 at 70 fps. c:
Before this I had an Nvidia 9400 GT (;-;) and I couldn't run anything modern above 20 fps on lowest settings.
I also got my quad core 3 ghz processor a couple days ago, yay. c: