If you don't mind build it yourself, I put one together a couple years ago based around a Xeon 5603 CPU. Used a Supermicro board, takes up to 24GB RAM (6x 4GB) Works fine for me, currently hosting (with only 12GB, bought another 12GB but haven't put it in yet):

1x Domain Controller

2x SQL2012 Servers (set up to play with Always On)

I had a couple others, but for now have them off.

Jason