Users of Unix and Linux are probably very used to virtual desktops; they've been present in the GUIs for those operating systems for a long time. Windows users, however, have been stuck with a single desktop - unless they use something like one of these five addons.
The first selection is Desktops from Sysinternals, a Microsoft brand. Desktops is a very simple implementation whose strongest feature is the on screen quick preview of the possible four desktops.
Screenshot of Desktops interface by Wally Bahny for TechRepublic