Microsoft offers Virtual Server R2 Enterprise Edition as free download!

Microsoft Virtual Server 2005 R2 is an ideal, production-quality tool for consolidating multiple workloads onto a physical server, allowing organizations to make more efficient use of their hardware resources. Built upon Microsoft Virtual Server 2005 SP1 and bolstered with new functionality, Virtual Server 2005 R2 enables IT organizations to enhance their administrative productivity and rapidly deploy new servers to address changing business needs through automated deployment and configuration of connected virtual machines that are easily administered with standard server management tools. Virtual Server 2005 R2 is an extensively tested and well supported virtualization solution that is supported both by the broader ISV community and by Microsoft in conjunction with its server operating systems and applications.

FYI, Virtual Server 2005 originally cost $999 and $499 for the Enterprise and Standard editions, respectively, when released in September 2004. Microsoft then released Virtual Server R2 at $199 and $99 for the Enterprise and Standard editions, respectively, in December.