A reader named Miranda (who, sadly, recently lost her camera on a trip) sent along a link to the terrific blog Found Cameras and Orphaned Photos. The concept, as you might imagine, is pretty simple: people who find cameras or memory cards email photos to the blog, and the photos get posted. If you’ve lost your camera (or if you recognize anybody in the photos), you can contact the finder through the blog to get your photos back.
I might have done the implementation differently (enabling people to search a database by location, date lost, etc), but it’s a good start. The site will become more invaluable once photo-matching and recognition technology becomes more available.