TopDesk : A super top desk application
I have always tried applications or tools like TweakUI and it's alt-tab replacement. With it, while you alt-tab through your applications, you see a small screenshot of that application. That way, it's much more clear which applications you're alt-tabbing through. Even better is the hotspot in the bottom-right corner, or any other corner you set it up for. You just move the mouse there, all applications become visible and you get to select one.
Now Scott Hanselman blogged about a tool called TopDesk. The idea seems to come from Mac OS X Expose, but now for Windows and written in Direct X. Where Tweak UI is really slow, TopDesk is blazing fast on computers that don't even have a nice Direct3D card. You can check out how it works in this video by Scott.