Sometimes my backup regime gets out of hand, so I made a simple script to find likely duplicates across multiple drives. Basically, if gives me a list of files that are the same size and same extension that are larger than 100 megs. There was some false positives, but not many, so even thought it outputs a batch file, I didn’t run it unedited:
ruby find_dupes.rb > dupes.bat
My drives were hooked up to a windows machine, hence all the windows-isms.