A few months ago I reviewed the performance and use of VirtualBox. A new version has just been released.
Version 2.1.0 is a major release and adds a whole new range of capabilities including:

Better hardware virtualization support on the Mac OS X operating systems

Better hardware virtualization support for Intel and AMD

full VMDK support

A better NAT engine

A [...]

VMWare Workstation has always been a pretty good desktop virtualization product. I first used VMware Workstation 3 back in 2004. Back then I used it for testing recovery scenarios.
The latest Workstation offering from VMWare shows why this product has managed to be so strong in the past. The key features in this version are: