Got this combo for my NAS build, SuperMicro X8DTT-F Motherboard with 2x Intel E5620 CPUs, can't complain for $50-USD. The board dimension is ~17"x7"; so it's easily hacked into a 4U or ATX case.
(http://i64.tinypic.com/1193vyh.jpg)
This board has an IPMI interface, allowing you remote desktop management over IP
Wiring is easy and straightforward.
Front panel wiring
(http://i68.tinypic.com/166m8ar.png)
Power pin outs
(http://i68.tinypic.com/11b8az8.png)