Virtual Iron (www.virtualiron.com) is a most impressive piece of virtualization software. It's very functional, and it's far less expensive than VMWare if it suits your needs. I recommend purchasing the web-based training as well.
As an added bonus, Virtual Iron includes a fancy software product called "Platespin Portability Suite" (now owned by Novell) that can convert a physical machine into a virtual machine (aka a "P2V conversion"). I performed a P2V conversion on a production server yesterday, and the Platespin software worked nearly flawlessly. The only thing I noticed that did not survive the conversion was my NTFS quota settings on the server's second volume, but that is a minor quibble.
All in all, I am very pleased with Virtual Iron and Platespin Portability Suite in helping my company transition from a physical to a virtual server infrastructure with a minimum of headache.
Now that Virtual Iron has been purchased by Oracle (as of May 13, 2009), it will be interesting to see what effects this has on the Virtual Iron product and pricing. I hope Oracle will continue to enhance the Virtual Iron product without raising its licensing and support pricing. If they increase the costs too much, they risk losing the customers on which Virtual Iron built their business.