Mobo: P67 chipset on an MSI military class mobo(under $100USD), unless you 'need' a z68 chipset in which case you should go with ASRock or Asus.
Ram: 8GB (2x4GB kit) of your favorite brand. 1333 is fine, or 1600 if you find a good deal. Just stay away from tall heatsinks as they can mess with your CPU cooler.
GPU: After you pick all parts get the fastest AMD card you can afford, unless you want physx or CUDA in which case you need to go nVidia.
Case: I like Thermaltake for cheap quality cases that dont look like they were designed by/for a middleschooler, but I am also a big fan of the HAF series, as well as some of inWin and Corsair's offerings, but that is a matter of personal preference. Bottom mount PSU is nice to look for though, as is tooless entry.
HDD: I would go for an SSD made by Intel, Crucial, or OCZ for a system drive, and hold off on a data drive until next year when prices come back down and manufacturers recover from the flooding. SSD's really bring a new level of expectations to your computer use.
CD/DVD: go get the cheapest blue ray player/DVD burner you can find. Never spend good money on optical media/drives
Power supply: Go with a 500W for a single GPU, 750W for SLi/xFire with med level cards, and 900+W for high end GPUs. I like OCZ and PC Power and Cooling (same company), but many like Corsair. Just be sure to get something heavy and with quiet fans and you cannot go too far wrong.
that should leave plenty of money for extra fans, aftermarket heat sinks, card readers, and other accessories you may want. already having the KMV and OS really opens your budget up to have some fun!