A lot has been said regarding the new "Exposé in the Dock" feature in Snow Leopard. Just click and hold on a Dock icon, and you'll get an Exposé view of all that apps open windows.
I am not sure if this is common knowledge or not, but if you Control-click (or right-click) on a Dock item, you get the pre-10.6-style pop-up Dock menus. They are the new white-on-black HUD style menus, but with the old functionality.
Extra credit goes to the person who finds out how to set this as the default behavior.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090828190428282