exposé using DWM API
Greg Schecter has been blogging extensively about the DWM API's in Windows Vista lately. It's definitely worth a look, as he does a great job outlining the possibility of what you can do using the DWM on Windows Vista.
One great example I saw recently was created by someone I only know as "Simon on .Net", who built an implementation of Apple's Exposé feature from OSX on top of the DWM in Windows Vista. Nice!