SnapSeeker is a photo site with a new contest every week. Upload a picture and the community rates it. The winner gets a prize (such as a GPS).
The site was built by Ericson Smith "a couple weeks to scratch an itch." The site spreads virally as users urge their friends to vote for them. Users can also place a widget on their own site promoting their pictures.
Snapseeker is a Rails application, and photos are stored on Amazon's S3 web service.