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.
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 indexes are stored internally.TO DO: Automatically mark duplicates as "rejected" and keep only one version of an image. Let me know if this feature is wanted!