Microsoft Senior director of virtualization and System Center, Zane Adam, writes on the TechNet blog:

Last Fall we released Microsoft Hyper-V Server 2008, a standalone hypervisor-based virtualization product that is available for free. We continue to add more features and value to this product in the upcoming release, Microsoft Hyper-V Server 2008 R2.  Our core strategy is to ensure that our customers can virtualize their IT environment in the most cost effective manner, and at the same time, have access to enterprise features like live migration and clustering features for high availability.  So in addition to scalability and performance improvements in this version, customers can get live migration and host clustering capabilities and high availability (up to 16 nodes) at no charge.

Microsoft Hyper-V Server 2008 R2 will continue to be free, and now will include live migration and host clustering capabilities. Customers won’t need to pay thousands of dollars for alternate virtualization platforms to get these features. With Microsoft Hyper-V Server 2008 R2, customers have a solution for both planned and unplanned downtime and can use it for scenarios like server consolidation, branch server consolidation, high availability, and VDI.

These same features also will be available in Windows Server 2008 R2 Hyper-v, which provides our customers with core virtualization features as part of Windows Server offering.  With Windows Server 2008 R2, customers also get flexible virtualization rights (e.g., 4 free virtual instances with Windows Server Enterprise Edition and unlimited virtual instances with Windows Server Datacenter Edition).

You can download Microsoft Hyper-V Server 2008 R2 beta here. Microsoft Hyper-V Server 2008 R2 can be managed by System Center Virtual Machine Manager 2008 R2. You can download the beta here.

You can find more info on Microsoft’s virtualization products and solutions at http://www.microsoft.com/virtualization.