I am sure you have seen these already, but if not, these are great tools to help when you quickly need a machine to test something on, or spend longer learning about a product.  I know you can get the disks in the action pack, but then you have to load it up on a PC or VPC - this saves you all the trouble.

Windows Server 2003 R2
Windows Server 2003 R2 helps to simplify branch server management, can improve identity and access management, helps to reduce storage management costs, provides a rich Web platform, and offers cost-effective server virtualization. In this VHD, you'll have the opportunity to road-test new and improved features and functionality of Windows Server 2003, including management and usability enhancements to Active Directory.

 

Exchange Server 2007
Learn how to take advantage of key features of Exchange Server 2007. This VHD provides an exploration of Active Directory and the new features in Exchange Server 2007, new features in Outlook Web Access 2007, enforcing compliance and retention policies in Exchange Server 2007, and more.

 

SQL Server 2005
SQL Server 2005 is data management and analysis software that helps deliver increased scalability, availability, and security to enterprise data and analytical applications while helping to make them easier to create, deploy, and manage. In this VHD, you will get to experience many of the new features in SQL Server 2005.

ISA Server 2006 VHD

This download comes as a pre-configured VHD. ISA Server 2006 is the integrated edge security gateway that helps protect your IT environment from Internet-based threats while providing users with fast and secure remote access to applications and data.

For a complete list of Microsoft products and technologies in a VHD, visit the VHD Download Center.

Source: Run IT on a Virtual Hard Disk