I have long had Exposé (Mac OS X) envy. Now you can get the love on Windows Vista with Switcher:
I would recommend editing shortcuts to add the mouse-in-the-screen-corner shortcut to better emulate the Mac Exposé behavior:
Settings > Shortcuts > Edit Shortcuts > Add Shortcut > Mouse Over Screen
If you have more than one monitor, you can create two mouse shortcuts, one for the top-left of screen 1, and the other for the top-right of screen 2.
Excellent tool. It also works great on a Windows Server 2008 workstation.