Snow Leopard introduced a 'click and hold' feature for app icons in the Dock, to reveal application windows with a new 'Exposé in the Dock' effect. But most keyboard lovers don't really think that's too useful.

However, you can activate the effect from the Command-Tab switcher by pressing the Down or Up keys while holding Command. After the Exposé effect appears, you can release the Up/Down keys, and then press Tab or Shift-Tab to choose from opened applications.

But choosing a window needs too many key presses: You must at least press one arrow key (Up, Down, Left, or Right) to make the blue focus box appear. After you choose a window, press Space Bar to Quick Look the window, or press Enter to bring the window to front. (Of course, you can hover and click if you reach for the mouse, too.)