DIY. Planning a Norco 24-bay case, Supermicro board with five 8x PCIe 3.0 slots, and 3 8-port LSI 2008 controllers. Intel supposedly "launched" their $300 E5-1620 processors over two weeks ago, but for some mysterious reason (*cough* profit) the only processors that are actually available are the DP variety that cost three times as much.
For software, I'm planning VMWare vSphere 5 with PCIe passthrough, but I'm still waffling between ZFS on FreeBSD or mdadm+LVM on CentOS 6. Right now leaning toward the latter.
I'm glad the hard drive prices have finally come down to reasonably sane levels. Although I certainly wouldn't mind if they dropped back to pre-flood levels before I end up buying a huge stack of them.