Archfinch was a website that let you rate things you like or hate and get recommendations based on what you like. At one point it had 80,000 monthly page views. It was pretty cool, but I shut it down in 2011 when I decided to focus on other things.
The site had a huge (scraped) database of video games, TV shows, movies, books, anime, manga, comic books, videos and links. Everything was tagged and it was possible to browse things similar to each other even without an account.
Django, PostgreSQL, Sphinx, Celery.