VirtualBox is a virtual pc emulator like vmware. It has many of the features vmware has, as well as some of its own. It is in constant development and new features are implemented all the time. eg. version 2.2 introduced OpenGL 3D acceleration support for Linux and Solaris guests. It has a nice GUI interface (Qt and/or SDL) or command line tools for managing virtual machines. Headless operation is also supported. Running iTunes under VirtualBox is the only way (currently) to sync iPod Touch/iPhone firmware 3.0+.
The following patch includes the changes I made to the Xorg XKB files adds a keyboard model for the MS Digital Media Keyboard that maps some of the multimedia keys: