On Monday at the "Get Virtual Now" marketing event Microsoft announced the stand-alone version of Hyper-alone will be completely free. The stand-alone version is essentially Windows Server 2008 Core with just the Hyper-V hypervisor role installed so there is no GUI for VM management on the server. Management tools can be installed on another computer to manage the server with a GUI. The special version of Hyper-V is expected to be released within 30 days.
Take that VMWare ESX server!