hii,,,i have bought a core i3-530 processor and its supported MOTHERBOARD INTEL DH55TC...
it has a hd graphic memory of 256mb inbuilt in it......and now if i wanna add the best and most compatible graphic card....which one would it be???
in your price range, you can look into the ATI 4850 and 5750. Nvidia has the GTS250 in that price range. They all have a similar performance and will work very well with your current monitor. The ATI 5750 offers DX11 but costs more then the 4850 & GTS250.
For $160, you can step up to the ATI 5770 which is a better card but makes more sense with a larger monitor.
GTS250 is a nice card for the money but if you want ATI with that budget its either a 56x0 or at best a 5750. Your PSU is a cause for concern with your build. Ware ever you have a little money stowed away scrap together another $40-50 and get a better psu like antec or enermax from off eBay or a local store. Quality is every thing when it comes to hardware.