TagFlow - TagFlow is an intelligent files manager that use tags for organize your documents.
TaggedFrog - Based on the convenient drag ’n’ drop technique, TaggedFrog allows you to organize your files...
Tagger - Tagger is a small application for OS X that can be used for quickly adding arbitrary textual tags...
One Commander - Your next file manager
Leap - With Leap you find things based on your natural memory of that file.
Elyse - The free version allows up to 30 tags.