I haven't had the problem of a frozen application on my Mac OS X laptop in a long time, but when it does I can never remember the keystroke combination to bring up the Force Quit dialog. The key combination is [Option][Command][Esc], which I know at this moment because I'm looking at it in a book.
Since I can't remember that combination I'm hoping this mnemonic will help: "Oh Crap Eddie", where "Oh" stands for "Option", "Crap" == "Command", and "Eddie" == "Esc".
Well, at least I can hope that comes to mind if an application ever freezes again. :)