Before you plunk down serious cash on an enterprise virtualization solution, check out the free, open-source ProxMox VE. It is based on two mature open-source virtualization products, namely OpenVZ and KVM. I maintain two physical ProxMox VE servers running a total of eight virtual machine “guests”, including Ubuntu 8.04, Ubuntu 9.04, Windows 2003, and CentOS. So far, the expirience has been nothing but positive.
There’s also a good review of ProxMox over at www.montanalinux.org.