This list includes only those sites that publish reviews of self-published books. (There are more sites for traditionally published books.) They all offer reviews for free, the only exception being RT Book Reviews. Some accept books for review, while others accept freelance reviews, in which case someone - not the author - would have to submit a review.
The advantage of a book review site, as opposed to a blog, is traffic. Most blogs can't compete with well trafficked review sites for the simple reason that most review sites rely on more than one reviewer. (Even blogs with two or three reviewers can't compete.) This allows review sites to cover more books, which, in turn, attracts more traffic.
Additional Resources:
Fantasy and Sci-fi Reviewers Accepting Self-Published Authors
A list of 269 online book reviewers who accept self-published work in speculative fiction (scifi, fantasy, horror, paranormal).
Top 5 Sites for Science Fiction Writers
If you write scifi, these are your go-to sites.
Top 20 Sites for Finding Reviewers
These are the best sites for finding reviewers in any genre.
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Strange Horizons
Strange Horizons publishes in-depth reviews of speculative art and entertainment, especially books, films, and television, three times a week. Reviews normally cover new works, they will not reject a review because its subject has been available for a while. "We're especially interested in reviews of worthy material that might not otherwise get the exposure it deserves; similarly, we are interested in reviews of works that push traditional genre boundaries." They pay $40 for a review.
SF Reader
SFReader offers reviews on any book, anthology or magazine that has a speculative element (all flavors of science fiction, fantasy, and horror). They prefer traditionally published print books, but will accept Kindle format.
Fantasy Book Review
This popular site reviews fantasy books only. They get a large amount of submissions per month, so a review is not guaranteed. (They review 1 in 50 submissions.) All books are read, reviewed, categorized and awarded a rating between 0 and 10. These ratings then determine who and what appears in the list of the Top 100 Fantasy Books. At time of writing the number of books that have been read and reviewed stands at well over 1,000.
Fantasy Book Critic
Fantasy Book Critic is a group of individuals devoted to covering Fantasy, Science Fiction, Horror, YA/Children’s Books and other Speculative Fiction. They accept review queries from publishers large, small and independent as well as self-published authors. Both print and electronic formats are accepted.
Lightspeed Magazine
Lightspeed is a well known science fiction and fantasy magazine. If you have a book you’d like them to consider for review, or you’d like to send a press release, use this address: reviewbooks@lightspeedmagazine.com All of their reviews are in-house.
Science Fiction and Fantasy World
Authors and publishers can fill out a request for a review on their contact form. Authors can also promote their books on the Promotion Zone. This site gets quite a bit of traffic. Their list of interviews, reviews, articles, and guest posts is extensive. They also publish anthologies.
Revolution Science Fiction
Revolution SF accepts book reviews from guest reviewers. "All reviews should be fair and well-reasoned. Feel free to rant if the subject deserves it, but make sure the justification for the rant is self-evident. If something sucks, say it sucks, but tell us why. If something is wonderful, say it's wonderful, but tell us why. Give a frame of reference."
SFcrowsnest
Everything on this site is contributed by readers. The areas they cover are scifi, fantasy, horror, steampunk, computers, anime, manga, games, RPGs, toys, models, science, futurism, films, TV. Electronic format press releases and articles/reviews can be sent to the editor, Geoff, via gfwillmetts-2 (at) hotmail.co.uk.
The Future Fire
The Future Fire accepts both freelance reviewers and suggestions for titles to review. "We will consider all subgenres of speculative fiction (and related nonfiction), regardless of author or medium, including self-published work, but we are especially interested in seeing more books by and about women, people of color, LGBTQIA, disabled people, people with nonwestern languages and religions, and other under-represented groups."
RT Book Reviews
This popular site reviews sci-fi and fantasy, as well as a number of other genres. You can submit a new release or a reduced price for your ebook. However, book reviews cost upwards of $425. (It's still a good place to send information about your book release.)
Bonus site
Tor.com
In addition to accepting novellas, Tor accepts non-fiction submissions, including reviews.