Budget Gaming PC

Looking to build a budget gaming PC that is upgradable for more high end performance in the future.

I want to limit the cost to as little as possible obviously. I have $250 already set aside to use and I have the OS and RAM. I will still need the CPU, GPU, PSU, Case, MoBo, HDD and Optical Drive. SSD, Monitor, Keyboard, Mouse, CPU Cooler is something my brother can aquire later.

I need help mainly on the GPU selecting one that is a good price and runs current games on medium settings well, averaging a decent FPS rate. It also needs to be able to support SLI/Crossfire so he can add an additional card on his own and allow him to play on more intense settings. So what are the best valued GPU's for a Crossfire or SLI setup that perform well enough on medium settings and benifit the most from adding an additional GPU?

Thoughts so far: Everything here is open for suggestions.

CPU: i5 3570k $219
GPU: ?
MoBo: ASRock Z77 Extreme 4 $119
PSU: Corsair HX750W $129
HDD: Seagate Barracuda 1TB 7200RPM 64MB 6.0 SATA $79
Optical: ASUS DRW 24x DVD-Burner $19

$565 before graphics card which I am expecting to cost around $200