Regular Websites
"Kirkus Reviews posts over 500 pre-publication book reviews every month in multiple genres." Well-established. Paid subscription required for full access; excerpts and short reviews available free. - Kirkus Reviews Online
http://www.kirkusreviews.com/kirkusreviews/index.jsp
One of the world's best known resources for science fiction, fantasy, horror and other news. The website also provides details on book reviews and awards given to science fiction and related works. Find out about new books in these fields using this website. - Locus Mag
http://www.locusmag.com/
Links to freely available professional book reviews from major media outlets, and the site's own reviews. 2002-present only. - ReviewsOfBooks.com
http://www.reviewsofbooks.com/
Large site of children's book reviews written and illustrated by kids for kids. Read their reviews or submit your own. - Spaghetti Book Club
http://www.spaghettibookclub.org/
The New York Times Book Review
Reviews, features, author interviews and book excerpts from the national daily and the Sunday book review of the New York Times. Free registration required. - The New York Times Book Review
http://www.nytimes.com/pages/books/