Switcher (in my opinion; THE only option atmo)

One of the most useful tools for Windows actually puts the beautiful Aero presentation system to good use.
The Mac has long had a fantastic Window switcher called Exposé. It
tiles all of the windows on-screen and makes it easy to switch from one
Window to another with only a minimum of key strokes. The Vista
equivalent, called Flip 3D is certainly pretty, but effectively useless. This is where Switcher steps in. Switcher is a clone of Exposé. Unlike other clones,
it uses the Windows desktop manager API (the same one used by Flip 3D).
This means that the preview windows are pretty, windows update as the
content changes, video plays and all is generally right with the world.

Switcher makes good use of Windows Vista Aero.