The new version of the Encyclopedia of Science Fiction (its 3rd Edition) started life as a print book, but rapidly became too large to be publishable in a single volume. As a result, the project became an online encyclopedia, a dedicated resource to all things SF.

The encyclopedia is a very impressive achievement from what I've seen so far. Flipping through articles, looking up TV shows, authors and computer games, this could replace TVTropes as the ultimate timewasting internet destination of choice

Note: this is the beta release of the encyclopedia, incorporating about 75% of the planned 'final text' (which they hope to reach by late 2012, though the encyclopedia will continue to be updated after that point). In addition, the encyclopedia is for science fiction and science fiction alone; the same authors will potentially tackle an online Encyclopedia of Fantasy (they previously published a text one in 1996) if the SF one is a success.