In almost every Mac OS X application/text field, the emacs keybindings (Ctrl-p,Ctrl-n,Ctrl-b,Ctrl-f for up, down, left, right, respectively) work. I, personally, very rarely use the arrow keys for navigating text.

Ctrl-a, Ctrl-e, Ctrl-k and Ctrl-y also all work for beginning of line, end of line, kill and yank.