I've just finished updating my Keyboard Shortcut Reference sheets for Adobe InDesign CS4. I've managed to fit all 375 or so shortcuts on two U.S. letter-sized pages. I like to have a printed copy of this handy by my computers at all times. I've given a lot of thought to how the shortcuts should be organized and grouped in this latest version of the Shortcut Reference. You may download a Macintosh version here, or a Windows version here, as a free PDF. You can also find versions for CS2 and CS3 here.
BONUS TIP: while researching the keyboard shortcuts for this project, I stumbled across one undocumented shortcut: On the Macintosh, Option+Enter (on the numeric keypad) inserts an "End Nested Style Here" character in both CS3 and CS4. Pretty obscure, but this might be useful for someone.