I built my PC for $600.
i5 2500K (With Cooler Master Hyper 212 Plus heatsink/fan)
NVidia MSI GTX 560 TI Twin Frozr II/OC
4GB Corsair 1333MHz RAM
1 TB HDD
550W PSU
DVD Burner
You just have to shop around and watch for rebates/coupons.
Edit* Also, this was 7 months ago.