I virtualization heaven! I am currently using VMWare Server on most of the machines I am doing virtualization on - but the fact that the Microsoft Hypervisor "Hyper-V" is available for free now is really cool:

"Microsoft Hyper-V Server 2008, a bare metal hypervisor-based server virtualization product, is now available as a no-cost Web download at http://www.microsoft.com/Hyper-VServer. Microsoft Hyper-V Server 2008 provides a simplified, reliable and optimized virtualization solution for customers to consolidate Windows or Linux workloads onto a single physical server or to run client operating systems and applications in server-based virtual machines in the data center. Microsoft Hyper-V Server 2008 allows customers to leverage their existing provisioning, updating, management and support tools, processes and skills."

Source: http://hypervoria.com/