Guess it will be on a lot of blogs today, but here goes anyway.
Hyper-V, Microsoft's hypervisor based virtualization product that is part of Windows Server 2008 went RTM today. In terms of public availability, it sould be available for download later today (12pm PST), with availability via Windows Update scheduled for July 8th.
Hyper-V Home Page here
Server & Tools blog
Virtualization Team blog