Keep track of the films and TV show episodes you have seen. Follow shows and have your own TV calendar, and never forget your favourite TV show episodes.
IMDb - Internet Movie Database
TMDB - free movie database
Flixster - Share movie reviews and ratings with friends.
Letterboxd - Letterboxd is a social site for sharing your taste in film, now in public beta.
Simkl - Simkl is a TV, anime, and movie tracker that keeps a history of all the shows and movies you watch in one, central location. It’s a mobile app, a website, Google Chrome extension to keep track of everything you watch and integrates with many TV apps
TheTVDB.com - An open TV series database that can be modified by anybody, and accessed vi an XML API.