If you are running Windows OS you might also want to check out
Deep Perspective.
Their keywording tool works as a photoshop plugin and includes:
Spell Checker.
Correction suggestions.
Synonyms suggestions.
Sorting.
Deleting duplicate words.
Words counting.
Saving groups of words and adding all the words in the group at once .
Saving complete Templates of Meta-data.
Converting words to upper/lower case.
Recent typing list for any Meta-data field.
You can download a trial version or purchase it for 15$. The trial verision is fully functional for 30 days.
I've been playing around with it for a couple of days and it seems to be very useful, especially for those pesky synonyms.