Mamadupe... Hunt down duplicate photos in your Aperture library! Mamadupe uses an advanced algorithm to remove all the guess work from the tedious task of finding duplicate photos and then conveniently tags them for your further inspection.
UPDATE 1.0.1 Fixes crashes on launch. Also, some users have raised issues about removed duplicates showing up on second launch. Your feedback is much appreciated!
NOTE: Indexing of the library is incremental. It may take some time on the very first launch (approx ~30 minutes for 50,000 images), but subsequent launches will only index newly added images as previous