Have you checked out our selected links in the far right column of the
science fiction/fantasy/horror page? I'd especially like to point out
SciFan, a database filled with thousands of titles and authors that allows you to search for books by themes, release dates, series names and more.
SF Site has tons of book reviews, author interviews and fiction excerpts.
SFF Net connects you to more than books if you're interested in writing speculative fiction yourself, or finding out more information about the SF community and its conventions.
This is just scratching the surface about what's available. Have fun exploring!