Spell checking cheat-sheet for emacs.

• M-$ - ispell-word or ispell-region (depending on whether something is selected)
• [SPACE] - Skip this word—continue to consider it incorrect, but don't change it here.
• r newword [RETURN] - Replace the word, just this time, with new. (The replacement string will be rescanned for more spelling errors.)
• R new [RETURN] - Replace the word with new, and do a query-replace so you can replace it elsewhere in the buffer if you wish. (The replacements will be rescanned for more spelling errors.)
• a - Accept the incorrect word—treat it as correct, but only in this editing session.
• A - Accept the incorrect word—treat it as correct, but only in this editing session and for this buffer.
• i - Insert this word in your private dictionary file so that Aspell or Ispell or Hunspell will consider it correct from now on, even in future sessions.
• m - Like i, but you can also specify dictionary completion information.
• u - Insert the lower-case version of this word in your private dictionary file.
• l word [RETURN] - Look in the dictionary for words that match word. These words become the new list of “near-misses”; you can select one of them as the replacement by typing a digit. You can use * in word as a wildcard.
• C-g X - Quit interactive spell checking, leaving point at the word that was being checked. You can restart checking again afterward with C-u M-$.
• x - Quit interactive spell checking and move point back to where it was when you started spell checking.
• q - Quit interactive spell checking and kill the spell-checker subprocess.
• ? - Help

Via the emacs FAQ.