Here's a slightly refined version of what I would do here:
Mobo: Gigabyte EP45-UD3R, $115 ($15 MIR)
CPU: E8500, $188
RAM: G.Skill Pi Black DDR2-800, $50
Heatsink: Xigmatek HDT-S1283, $37 ($10 MIR)
Backplate: ACK-I7751 Retention Bracket, $8.49
Thermal Paste: IC Diamond 7 Carat, $7
HDD: Velociraptor 300GB (HLFS version), $230 ($30 MIR)
Optical: Samsung SH-S223F, $24
Case: Coolermaster CM-690, $90
PSU: PCP&C Silencer 610, $100 ($30 MIR)
Extra Fan: Scythe S-Flex SFF21F, 1600rpm (for the roof), $15.49
Total:
$865 before $85 of MIR
You could even add a Blu-ray reader and still fall within your budget.
For pure gaming, two cores is sufficient IMO and the 9800GX2 card is actually well matched to your 1920x1080 resolution.
I've also thrown in a Velociraptor for even more speed.
With an E8500 as spec'd above, aim for FSB of around 450 MHz at full multiplier and RAM at synchronous 1:1.
I think that you'd be pretty happy building around either the E8500, Q9650 or the PII X3 720.