While I certainly like OS X’s built-in spell-checking tools, I also find it somewhat annoying because it requires the mouse—first to click on the misspelled word, then again to choose the correct spelling. OS X Hints reader
Zonker.in.Geneva points out that you can actually use the keyboard to correct spelling errors in programs—such as TextEdit, Mail, and iChat (or Messages)—that use Apple’s system-wide spell-check system.
For the trick to work, you must first enable two options in each program’s Edit -> Spelling and Grammar menu: Check Spelling While Typing (the While Typing part may be in a submenu) and Correct Spelling Automatically.
That done, when you misspell a word, press the spacebar to insert a space after it, then use the left arrow key on your keyboard to move the cursor back so it’s immediately after the misspelled word’s last letter. If you wait a second, you’ll see a list of suggested spellings appear. Using the up and down arrow keys, select the spelling you want from the list, then press Return. That will replace the misspelled word with the correct spelling. If you want to dismiss the pop-up, press the Escape key.
While this keyboard navigation doesn’t work in all programs—it won’t in Microsoft Office applications, for example—you may find it works in many of the apps you use regularly.