Dexpot is a truly excellent, and free, virtual desktop system.
It provides an expose-style overview of all the applications running on a given desktop, a screen that shows all the desktops and configurable system tray icons that include buttons for each desktop or next/previous buttons.
You can instantly swap to a given desktop via Alt+1 for desktop 1, etc.
It also provides a rule-based mechanism for (amongst other things) defining which applications should automatically go to which desktops, including specifying whether focus should move to that desktop when the application is opened.
It even takes over Alt+Tab so that you only see those windows that are on the current desktop.
All in all, the nicest virtual desktop setup I've seen for Windows.