spell checking and "did you mean?"

Hi All I am looking to check whether a keyword a user has entered already exists in the database I can find exact matches, but I am having trouble with typos. I am looking for something like Google's "did you mean" if you type in a close match. SO if someone types in saet it returns "did you mean seat ?" Any suggestions which is best - SOUNDEX in MySql or the php functions levenshtein(), soundex(),metaphone() or similar_text() on the returned result. Any other suggestions welcome. Thanks Peter