a guy at work just told me about virtual box, which is free. anyone used it?
I'm using it on Linux but it's actually cross platform (Windows, Linux, MacOS, Solaris...).
It's on par with the consumer products of VMWare (Server or Workstation). In my opinion, it's quite fast and less bulky than its VMware counterparts.
At a company level, I'd rather choose VMWare ESX server (expensive) or Xen based virtualization.