Umm... Let me see... Anything from nVidia is the best. That's what all the major computer makers are going to now. I would say build your own computer with the most compatable parts. Get a nVidia mother board with Quad SLI Tech. Those things have major over clocking. I have it in my home computer, I have a 8 Gb Sli.
http://usa.asus.com/Product.aspx?P_ID=q8RE9mdlDnDHRRRR
Go to that site. I has one of THE best mother boards. It has 4 DIMM, Max 8 Gb DDR3. But i reconmend that you get a 64-bit os cause of reasons listed on the page. So yeah. Build your own. Get that mother board. Expencive, but the best.