We've talked plenty about the importance of learning basic keyboard shortcuts. If you really want to dig into some of the more obscure navigation shortcuts of OS X, writer Matt Gemmell has you covered.
Gemmell's guide touches on all kinds of different shortcuts, but the main emphasis is on navigation. This starts simple enough with tips on moving between apps (Command+tab and windows (Command+'). Then it moves on to navigating specific screens like the Save sheet screen, recent item submenu and more. It's a handy guide if you're already familiar with OS X's common shortcuts and are looking for a few more tricks.
Mac keyboard shortcuts [Matt Gemmell]