Media from FTP: similar to Media Sync, and is helpful way to scan and index files in uploads uploads folders. (update: doesn’t seem to work)
Media Deduper: nice way to look for duplicates.
Media Clearner: this one has a premium version which seems more useful.
Upload Directory Cleaner: this looks very untested.
Media Sync: this is very useful way to scan for items in the uploads folders that aren’t indexed in the media library.