MOBO - x48 chipset which will allow for full x16 in xfire.
ASUS RAMPAGE FORMULA LGA 775 Intel X48 ATX Intel Motherboard
http://www.newegg.com/Product/Prod [...] 6813131284
CPU - there are faster cpu's but this one can be OC'd comfortably to 3.5ghz
Intel Core 2 Quad Q9550 Yorkfield 2.83GHz 12MB L2 Cache LGA 775 95W Quad
http://www.newegg.com/Product/Prod [...] 6819115041
Heatsink -
XIGMATEK HDT-S1283 120mm Rifle CPU Cooler
http://www.newegg.com/Product/Prod [...] 6835233003
and
XIGMATEK ACK-I7751 Retention Bracket
http://www.newegg.com/Product/Prod [...] 6835233019
GPU -
SAPPHIRE 100251SR Radeon HD 4870 X2 2GB 512-bit (256-bit x 2) GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102768
RAM - DDR2 800 @ 1.8v. anything else is overkill with little to no advantage. 2 kits for 8 gb
mushkin 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory
http://www.newegg.com/Product/Prod [...] 6820146731
HDD #1 - pure speed. use for OS and games or frequently used apps that are resource hogs. OS = 10-20GB, Games = 50-100gb if you load 3+, most used apps = 20gb. High end you will have used 140gb of the 300gb available. + you have 1TB for every day stuff and another 1TB for backup. or you can use the whole 2TB for additional storage but I would lose my mind if I have over 1TB of data that was lost because I didn't back it up.
Western Digital VelociRaptor WD3000GLFS 300GB 10000 RPM 16MB Cache SATA 3.0Gb/s Hard Drive
http://www.newegg.com/Product/Prod [...] 6822136260
HDD #2&3 - storage and backup
Western Digital Caviar Black WD1001FALS 1TB 7200 RPM 32MB Cache SATA 3.0Gb/s Hard Drive - OEM
http://www.newegg.com/Product/Product.aspx?Item=N82E16822136284
PSU- room if you ever decide to xfire or jump up in the next generation of cards.
CORSAIR CMPSU-1000HX 1000W ATX12V 2.2 / EPS12V 2.91 SLI Ready CrossFire Ready 80 PLUS Certified Modular Active PFC Power Supply - Retail
http://www.newegg.com/Product/Prod [...] 6817139007
CD/DVD Burner - ummm, I just picked 1 with a high rating get 2
LG Black 20X DVD+R 8X DVD+RW 16X DVD+R DL 20X DVD-R 6X DVD-RW 12X DVD-RAM 16X DVD-ROM 48X CD-R 32X CD-RW 48X CD-ROM 2MB Cache SATA 20X DVD±R DVD Burner w/ SecurDisc Tech - OEM
http://www.newegg.com/Product/Prod [...] 6827136149
Case - its big and has good airflow
Antec Twelve Hundred Black Steel ATX Full Tower Computer Case - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16811129043
OS -
Microsoft Windows Vistahttp://en.wikipedia.org/wiki/Windows_Vista Home Premium SP1 64-bit English for System Builders 1pk DSP OEI DVD
http://www.newegg.com/Product/Prod [...] 6832116488
Monitor - Acer P243WAid Black-Silver 24" 2ms(GTG) HDMI Widescreen LCD Monitor with HDCP Support 400 cd/m2 3000:1 ACM - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16824009125
I didn't include a keyboard or mouse. Total price before mail-in-rebates and shipping = $2906. I did not use DDR3 because it is overpriced and there is little to no performance gain.
Last thing, with your budget I would wait 1-2 months and get the new i7 cpu's.