I have the print editions of both The Encyclopedia of Science Fiction and The Encyclopedia of Fantasy. Both are excellent, masterful works, full of isightful information about writers, their works, trends within the genres, and more.
The latest incarnation of The Encyclopedia of Science Fiction will be online. The entries will be even longer and more comprehensive since the editors won't be limited because of page length (the print copies are enormous books).
It's not available yet, but if you'd like to sign up for an e-mail newsletter about the project, go here.