The Internet Speculative Fiction Database: Contains a fairly comprehensive history of publication for many -- if not most -- science fiction and fantasy books and magazines. Extremely useful if trying to identify bibliographic information for older works, or past editions of reprinted works.
The Science Fiction and Fantasy Research Database: Run by Texas A&M's University Library, this database allows scholars to search for critical works that have been published on certain sf authors or topics. This database indexes works published in scholarly journals as well as reviews of sf books.
The Encyclopedia of Science Fiction : What it says on the tin.
Academic Journals focusing on Speculative Fiction:
Foundation: The International Review of Science Fiction
The Internet Review of Science Fiction (Dead as of February 2010, but all their content is still online.)
The New York Review of Science Fiction
Science Fiction Studies
The SFRA Review
The Arthur C. Clarke Center for Human Imagination
The James Gunn Center for the Study of Science Fiction
The International Association for the Fantastic in the Arts
The Science Fiction Foundation
The Science Fiction Research Association
The Speculative Literature Foundation
The James Gunn Center for the Study of Science Fiction at the University of Kansas
Science Fiction and Technoculture Studies at the University of California Riverside