CPU- E7300 $130
Mobo- Gigabyte UD3-P $115 after $20 MIR
RAM- Patriot Extreme 4gig (2x2) DDR2 800 $29 after $25MIR
PSU- PC Power and Cooling 500w 80+ certified $60 after $15MIR comes w/ free 4gig thumbdrive
GPU- Sapphire 4830 $100
Optical Drive- LG DVD burner w/ Lightscribe $26
Case- Coolermaster 590 $60
Heatsink- Sunbeam Corecontact Freezer $30 after $10 MIR
Total after MIR- $550
This will allow for some very good overclocking with the 45nm cpu along with the best OCing mobo out and an aftermarket heatsink that performs well. If you want a better heatsink you can upgrade to the Xigmatek S1283 for $7 more.
You can also substitute out the gpu and get this XFX 9800GT for the same price after MIR and it comes with FarCry2 game.
Looking over this again in referrence to OCing. I think it looking pretty good, but would add $30 for a decent after market CPU cooler.
EDIT: oops there is one..Great build here..