Yod'm 3D is a virtual desktop manager that allows you to have 4 different desktops arranged on a 3D cube.  Holding down CTRL+SHIFT and using the left or right arrow keys rotate the cube showing the virtual desktops. Alternatively, you can click and drag your mouse to switch desktops.

Video: TweakVista.com demo of Yod'm 3D *

* Because of the capture software I used, the video is very choppy.  Normally, the cube spins very smoothly.

Download this free desktop manager from Chris' Soft.

Update: Yod'm 3D Desktop was sold to a commercial developer and is now called DeskSpace.  Additionally, DeskSpace is no longer free but you can find a copy of the old freeware version here.