GadgetTrak's CameraTrace service helped a professional photographer get back $US9,000 worth of stolen gear. CameraTrace can also help you recover your lost or stolen camera, as well as find people using your photos without permission.
Like previously mentioned StolenCameraFinder, CameraTrace works by searching photos uploaded online for your camera's serial number. (Most cameras embed the serial number information in the EXIF data of every photo taken with that camera. CameraTrace has a list of supported cameras here.)
You'll need your camera's serial number to do the free search (so you can't simply upload a photo to do the search, as you can with StolenCameraFinder). The serial number is found on the camera itself and the camera box, so if you still have either of those on hand, now is a good time to write the serial number down just in case.
CameraTrace comes with a couple of advantages over similar services. For one thing, CameraTrace claims access to a much larger database of photos than its competitors. Also, if you register your camera for a one-time $US10 fee, CameraTrace will actively monitor the web for photos from your camera once you report it missing -- saving you the hassle of repeatedly searching via other sites. Once it finds anyone trying to upload photos from your camera, CameraTrace will notify you by email.
One final benefit for professional photographers is copyright protection: The image monitoring service shows you where your photos are being used, perhaps without permission.
You might not have $9000 worth of camera gear to protect, but for many this will still be worthwhile insurance.