Xeon e3-1231v3 http://ark.intel.com/products/80910/Intel-Xeon-Processor-E3-1231-v3-8M-Cache-3_40-GHz
If you can't find that one, the 1230v3, 1240v3, and 1241v3 are similar.
If you need integrated graphics, the 1245v3 or 1246v3 are great.
Beat me to it. Newegg has the Xeon E3 1230v3 for $249. This is going to be your best bang for the buck. It's the same as an i7 4770 minus the integrated graphics and it's 200MHz slower. But it gives you hyperthreading for the price of an i5 4670k.