This is the one I first got. All you have to do is upgrade the GeForce GTS 250 to a better one, so that the performace isn't bottlenecking in games. I got about 600 FPS in Minecraft on max settings with the GTS though.
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=2021639&CatId=2628
Oh, and it is listed as coming with 500GB HDD, but in reality it comes with 1TB!