I discovered a nifty little trick today. I’ve tested this in MarsEdit, mail and text edit, under 10.4 Tiger, but I don’t know what other apps it works with, or if it works in previous versions of OS X.
If you are typing something and you hit the ‘escape’ (esc) key midway through a word, a drop-down list will appear giving you all the possible options to complete the word. that’s just awesome. If I don’t know how to spell something, I usually just type it wrong, in order to access the other possible spellings through right-clicking the misspelled word. Now I can save a step.