Microsoft Hyper-V Server 2008 R2 SP1
Totally free, optimised for virtualisation, but with everything that’s on a Hyper-V solution based on Windows Server 2008 R2 SP1 Enterprise Edition (Failover Clustering and Live Migration).
Overview here, download it here. and learn how to deploy and configure it here.
Windows Server 2008 R2 with built in virtualisation
Watch my six minute introduction webcast here.
And my ten minute installation and configuration webcast here.
Read Gerry Forde’s Hyper-V training recommendation here.