Ever found that you have downloaded the same file multiple times?
This applescript droplet, dupcheck - identifies potential duplicates of a file using Spotlight metadata, simply drop a file on the icon and the search will run, it may take 30 secs for a large drive. You will then get a list of duplicates (if any) and the option to show where they are in Finder windows.
It is based on a hint from macosxhints, see http://www.macosxhints.com/article.php?story=20061003163429425
For more information on Applescript have a look at the Applescript Resources Page.