Mastering the keyboard will not only increase your navigation speed but it can also help with wrist fatigue. Here are some OS X shortcuts to help you become a keyboard ninja.
Global Menu Shortcuts
(1) Fn-Arrow Keys is the equivalent of the Home/End and PageUp/PageDown buttons on a PC; Left-arrow and right-arrow for Home and End, Up-arrow and down-arrow for PageUp and PageDown.
(2) Fn-Delete deletes one character to the right of the cursor, same as forward-delete on a PC.
(3) Ctrl-F2 moves focus to the Menubar. You can use the arrow keys to select menu items and enter to apply them.
(4) Ctrl-F3 moves focus to the Dock. You can navigate around with the arrow keys to select applications and enter to switch to them.
(5) Ctrl-Cmd-D displays a popup dictionary for a selected word. Just hover over the word with the cursor and hit the shortcut. Useful for quick definitions.
(6) Cmd-Q quits the current application.
(7) Opt-Cmd-Escape opens the force quit menu where you can selectively force quit applications.
(8) Holding Shift-Cmd-Opt-Esc for three seconds force quits the frontmost application (Leopard and Snow Leopard only).
(9) Ctrl-Eject opens the shutdown/restart/sleep dialogue.
(10) Ctrl-Shift-Eject puts the display to sleep immediately.
(11) Opt-Cmd-Eject puts the computer to sleep immediately.
(12) Ctrl-Opt-Cmd-Eject shuts down the computer immediately.
(13) Enter renames selected file.
(14) Cmd-O opens the selected folder in the Finder.
(15) Shift-Cmd-N creates a new folder in the current directory.
(16) Cmd-J opens the View Options panel, where you can tweak settings for how a specific folder appears in the Finder, such as icon size.
(17) Cmd-I opens the Get Info panel for the selected item.
(18) Cmd-Delete sends selected file(s) to Trash.
(19) Shift-Cmd-Delete empties the Trash with confirmation.
(20) Shift-Opt-Cmd-Delete empties the Trash without confirmation.