The PSU is the backbone and mail component of any system, do not skimp on a PSU. For the 300.00 range the E8400 and the Gigabyte GA-EP45T-UD3P using DDR3 memory or the GA-EP45-UD3P uses DDR2. Either board offers you a stable and upgradeable MB.
With the prices of DDR3 being semi reasonable now I prefer the GA-EP45T-UD3P. It offers you 3 PCI-Express slots ( 1 PCI Express x16 at x16, 1 PCI Express x16 at x8 and 1 PCI Express x1) 8 SATA 3GBs, 8GB total memory (64bit OS) 1600 FSB/1333MHZ, 8 plus 2 USB 2.0
This board will also allow you some monster overclocks. Pollock1 got this system from me and we were able to OC it to 4.25 GHZ stable, it did run a little warm but yet was still stable. The E8400 on this board is an easy 24/7 3.6GHz with a FSB of 1800 to 1940 (depending on memory used)
TD