One of the refinements in Snow Leopard is a slightly under-the-radar trick for using Exposé from the Application Switcher. The Application Switcher is a quick way to jump between open applications, similar to the Windows Alt-Tab (at least that's what it was last time I used Windows). On a Mac, it's triggered by holding down the Command key (next to the spacebar) and then tapping the Tab key.
Subsequent taps of the Tab key will start selecting the next app in the row of applications, ordered by their most recent usage (so the last application you switched from is one Tab away). Shift-Tab moves backwards through the list. You can also navigate using the left and right arrow keys ... and, with Snow Leopard you can press the up or down key to show all of the windows of the selected application using Exposé.
Once Exposé is up, you can navigate the open windows using the arrow keys, and press Space to temporarily zoom a window for closer inspection. Pressing Return will switch to that application, with the selected window in the foreground. Escape will cancel the whole deal, dropping you back to your current working window. Also, once you've entered Exposé from the Application Switcher, it behaves just like Dock Exposé, and pressing Tab will advance to the next application in the list and Exposé its windows. See the video below for a quick demo, noting that the window zoom is triggered with Space, which isn't shown in the keyboard HUD on the video.
Thanks, Alexandre and Jonathan!