Right now im using a i7 920 with 12gb corsair 1600, and a gtx 285 superclocked and it runs very smoothly, you should look into a 750w power supply or better to push it. I went a little crazy with the video card, you really could go with a gtx 275 which is like $150 cheaper and will only be a few fps slower. As far as ram I wouldnt bother with 6gb as its so cheap now lol. Go straight for 12 than you dont gotta worry about upgrading later. As far as brands i like going with stuff that has great reviews, won awards etc etc, everything in my case is evga, and corsair, with the exception of the intel chip lol, o and the coolermaster v8 ive got chilling my chip.

Intel 920
coolermaster v8
evga board (lifetime warranty!)
corsair ram
corsair 850 power supply
evga gtx 285 sc