I found this quick helpful tip that works on Snow Leopard… and possibly Lion (but I haven’t tested that yet).

When you are switching through your apps using the “cmd-tab” keystroke, it can be frustrating that after selecting the application that you want, you still have to figure out which window is the one that you are hunting for… Well not any longer. While switching through your applications, simply press the “Up” or “Down” ¬†arrow keys on your keyboard to reveal the Expos√© display for the application that is currently selected. Then Boom, you have immediate access to the window you are searching for.