I am doing it without a SAN at the minute on a HP DL 380 G5 with 20GB of RAM and 2x 2.5 Quad Xeons. I'm about to hit the limit on internal storage - currently RAID 1 for 2008 R2 w/ HyperV @ 146GB and RAID 5 for storing VMs @ ~300GB. It currently running Exchange, 2008 R2 DC, WDS, Print Server, LANSweeper (Software Auditing), SharePoint 2010 Foundation, Sophos Server, WSUS Server.
This summer we're going to expand it with a Dell EqualLogic and another HP DL 380 G6.
On a basic level you just need a Server that can support Hardware Virtualization, be it Intel or AMD, most modern servers will support this, as with everything the more RAM the better, but don't think you need to spend £8000 on 144 GB of RAM, our current box started with 8GB, then 16GB, and now 20GB