Well.... I see you have a northwood CPU with DDR RAM right now. That's socket 478.
Core 2 Duo is socket T (LGA775) and requires DDR2 RAM. If you want a board that supports Core 2 Duo, you'll need a new CPU and RAM also.
But ok, you might already be prepared for the rest of the rig, so here we go:
$142.99 + $6.13 shipping = $149.12
Pro: excellent overclocking results, good overall board
Cons: no dual graphics, lacks RAID on the southbridge
ASUS P5B Deluxe
$194.99 + $6.94 shipping = $201.93
Pro: one of the best overclockers out there, excellent board, can do Crossfire and SLI (with modded drivers)
Cons: Crossfire/SLI only at x16, x4 mode.
Reasonable boards with the 975X chipset will cost a bit more. My DFI board is more or less in your price range, but I would not recommend it, esp. if you're looking for a board that can get you a high FSB (which you want if you're getting a E6300 or E6600). Also, the latest BIOS has limited overclocking functions, but there is a beta BIOS out there that gives more options. Only reason I got it is that I run Crossfire, and needed a cheap board to carry me over until DFI's RD600 board comes out.
finally, what is the total budget for your Core 2 Duo rig, and which parts do you plan on getting? Maybe we can help you with the entire rig.