Intel Xeon X5260
A dual-core "Core 2 Duo" based Xeon with 2 cores running at 3.33GHz. A nice performing server CPU back in late 2007 if you didn't need more than 2 (or 4 in dual CPU configuration) cores.
If you wanted 4 cores per CPU you could opt for the Xeon X5365 with the Clovertown core. It would set you back around an additional 500-600$.