I just read the handy QuickTime Player 'JKL' hint (fast rewind, stop, fast forward), and thought I'd run through the keys to see what else might be there.
I found another shortcut that doesn't seem to be documented anywhere: Tab will move you through the hour, minutes, and seconds fields, allowing you to jump directly to any time in the movie.
[robg adds: If you have 'All controls' set in the Keyboard Shortcuts panel of the Keyboard & Mouse System Preferences panel, you'll also tab through the playhead controls, as well as the individual controls at the bottom of the interface. If you have this feature set to 'Text boxes and lists only,' then Tab will just highlight the time fields, followed by the playback position cursor. I've only tested this in the Pro version of QuickTime, but I assume it works with the free version as well.]
Mac OS X Hints