Check out Witch:
Have you ever wanted to switch to a certain window — not just the application it belongs to? While you can use Exposé to switch windows, doing so can be very clumsy if you’re the keyboard-only type of user. And don’t all of these windows look just the same when they are scaled down?
Witch lets you access all of your windows by pressing a shortcut and choosing from a clearly arranged list of window titles.
Pretty cool and free. Originally spotted over at fscklog.