I just finished ordering my winter-break build. Came out to a bit more than $600, which isn't bad at all.

Gigabyte 790GX ATX motherboard
AMD Phenom II X3 720 Black Edition
Sapphire Radeon HD 4890 1GB
4GB G.skill DDR-1333 Dual Channel RAM
Western Digital Caviar Black 500GB HDD
Antec 200 Mid Tower Case
Reused: 650Watt Antec TruePower PSU
Reused: Some DVD-RW drive that's legit
Reused: Sound Blaster Audigy sound card

Still need Windows 7 and a monitor. Saved a good amount by scavenging old parts.

Wish I had a bit more for quad-core and I wish I found a good deal on a GTX 275 but there's nothing wrong with the rig that's coming up.