dalauder :
Have you decided on your other parts? Don't go cheap on the PSU. Get a good brand (or at least not a terrible one).
With that said, the cheapest ASUS mobo will get it done for you.
I'd get a better video card for slightly more money--maybe a GTS 450. That will assure that you can play casual games on low settings in 2 years instead of struggling with low settings now.
I'd drop the Phenom II x6 for a Phenom II x2 & unlock it or get the Phenom II x4 965BE C3 Revision and OC it to 4.0GHz. According to professional programmers I've talked to, we're not close to seeing many apps go multithreaded so the benefits of more than 3 cores is probably negligible. Although some programs, like Photoshop, use lots of cores. Save money and put it where it'll matter--in your video card.
RAM: Pay attention to the Latency. I'd get DDR3 2000 CL9 or DDR3 1600 CL6 with the money saved on the mobo or processor.
HDD: Samsung Spinpoint F3 1TB--nothing competes with this drive on a price to performance basis.
I already have the processor, HDD, case, and PSU. I want to build a machine that's going to last a long time, so I don't mind spending a little extra money to get a bit above what my current needs are. I have a OCZ 550w PSU, the phenom IIx6 1090t processor, western digital 1tb 7200 rpm sata 6 HDD, Cooler Master Haf 912 case.
I am buying the rest of the parts this week: the video card I mentioned in the prior post (which I might consider upgrading if it will make a difference for my usage - remember, I don't really play games, but I would like to hook up PC to my 46" TV), mobo I mentioned previously, 16gb (4x4gb) Gskill ripjaw DD3 1333 CL9, Windows 7 Ultimate, Cooler Master Hyper 212+ CPU cooler, and an additional 200mm fan and another 120mm fan (My case comes with 2 - 120mm).