Phenom II X4 955 Black Edition
Overclocked to 3.6 GHz
OCZ DDR3 1600MHz memory running 8-8-8-24 timings
ASROCK M3A770DE - The downside to this motherboard is that you can't run a crossfire setup at full speed because the ports are 16X and 4X not 8X and 8X
Antec 300 with 3 additional fans
PC Power and Cooling power supply 680Watts or higher
Hard drive is up to you depending on how much you want to spend and how much you need to store but for good speed and plenty of storage. I reccomend 2 500GB drives running in Raid 0. If you want your drive to be even faster you could buy one large drive like a 1 or 2 TB drive then just run windows or whatever you want to load fast from a solid state drive. Personally I have an 80GB Raid 0 that windows boots from and an extra 750GB drive for storage.
Get a 4890 for excellent frame rates in games. OR if you've got the extra money left then I suggest 5870 - this card is rather large so make sure your case is big enough.
With that size budget many people would suggest buying a Core i7 PC. Personally I think they are overpriced but there is no denying their performance.