Although I spend most of my `virtulsation and consolidation` time in the high end Unix/storage land (IBM PowerVM,VIO,WPAR,WLM- Oracle/Sun LDOMs,Containers/zones... USP-V HDP)
I do also use and keep an eye on developments in the x86 arena and run liveCD images such as network security toolkit ( http://downloads.sourceforge.net/nst/nst-vm-2.11.0.i586.zip ) or f5 BIG-IP ( https://www.f5.com/trial/ ) its a good quick and dirty way to get tools on your work PC without perverting it from its SOE image
For a good free hypervisor based virtulisation have a look at Xen(Ctrix xenserver) ,VMWare ESXi, Oracle Virtual Box and Microsoft Hyper-V
VMware options considered.....
ESX Server vs. ESXi ( http://www.vmware.com/products/esxi )
And there is always VMware player!
Oracle(Sun) Virtual Box
I also like some non hypervisor (ie emulators) eg QEMU www.qemu.org and bochs.sourceforge.net and www.winehq.org
Ive used QEMU quite a lot(in Windows to run Linux and via versa) and I would like to get an AIX POWER CHRP image working in it one day.
Some people are having a crack eg http://firstname.lastname@example.org/msg11382.html