NETWORKWORLD has a list of 10 noteworthy virtualization tools. Best thing of all, each tool they mention is available for free. Quite a good list of valuable freebies.
Here's one more: Altiris, now part of Symantec, offers their new Altiris(R) Software Virtualization Solution(TM) 2.0 also in a free version for private/personal use. Go to http://juice.altiris.com/svs.