Good luck buying your graphic card!
Also, just to remind you, you will want to buy an graphic card that has its second number "5" or more (for AMD) if you want to do "any" gaming, even the less demanding ones.
For AMD = x5xx or better (eg. HD 5550, 5570, 6570, 6670)
For nVidia = x4x or better (eg. GT 240, 440, 540)
However, AMD Low-End cards usually are more power-efficient and produces less noise than its nVidia counterparts.
Also, an AMD card that has its second equal or higher than "7" will need an 6-Pin PCI-E power connector. (eg. 5750, 6770)