VMWare is replacing their GSX line with a product called "VMWare Server" and it will now be free. I'm planning to build a new test server at home before too long and I think I'll give it a go. I was planning to use MS Virtual Server 2005 but I want to give this a try and see how it goes.
If you don't want to run VMWare on a host operating system, you will still need to purchase ESX. I'm guessing VMWare is starting to feel some pressure from Microsoft in the virtual server market.