You may want to check out
Dupin from
Doug's AppleScripts for iTunes, which is a great resource for managing your iTunes tags and files.
However, there are reasons why you may want to keep some duplicates. iTunes considers items duplicates if the song name and artist fields match. They may be from different albums, have different lengths or bitrates, be different file types, be live or studio versions, etc. There is no software that can make all those determinations for you. The safest method of dupe deletion is manual. With any other method, you run the risk of deleting something you didn't intend to delete.