I grabbed a few cheap Xeon E5-2670 chips from eBay. Man they are incredibly cheeeaap now! (slightly over $100 as of today) Eight cores, at the price of an A10 APU. With a decent X79 board one can get extreme performance. And I got a pair of them for a dual Xeon rig. 16 cores, up to 3.3GHz, 40 MB cache, octa-channel DDR3-1600, plus two mini SAS ports. It is simply a beast! And you get it below $1200!
Gigabyte GA-7PESH1, the SSI/EEB form factor dual LGA2011 server board, above all, is BLUE! Amazing as a server board, because almost all non-Gigabyte options are green and ugly. I saw a cheap deal on eBay and I got it without thinking twice.
NZXT Phantom. The legend. Not sure what inspired the designers, but my first impression was certainly the brave and loyal Imperial Stormtroopers. I decided to add some flavor that could awake the Force in you.
You will need a bit of case modding to fit a server board into Phantom. The hardest part is to get the power supply cables through the narrow groove on top of the case. It should be a huge problem if you already have a powered drill in your toolkit.
Zalman CNPS9900 series CPU cooler has been my favorite. They are round, meaning that the outline is contracted enough not to be an obstruction of anything on the motherboard (memory slots, the other CPU, etc.). And they are beautiful when paired!
As a geek of dual CPU configuration, I have built up around 10 such rigs. This isn't the most powerful one, nor is it the cheapest. But since I have mastered the in and outs of dual CPU, this is likely my most mature work. I finalized the machine by putting a Stormtrooper decal on it. Can you feel the Force now?