asahi.com BOOK http://book.asahi.com/
This website can be searched by keyword or theme.  Also includes interviews with authors, articles related to publishing, and information on the top-selling books in Japan.

 Book Review Map http://senya.pictopic.info/
This site allows you to search by topic, find relevant books and then find book reviews.

Japanese Book News http://book.asahi.com/
The Japan Foundation publishes a quarterly review of new books in Japanese which is also available as a pdf file.  Includes an evaluation of publishing trends, interviews with Japanese authors and reviews of new titles.  Full bibliographic information and price is included.

Kōdansha book club http://book.asahi.com/
Includes reviews of books published by Kōdansha published in national newspapers.

New York Times Book Review Archives http://book.asahi.com/
This is a full text archive of book reviews published in the New York Times since 1980. It covers over 50,000 books and authors, in reviews as well as in news and interviews.

Book Reviews in Scholarly Journals:

English language journals:
The Harvard Journal of Asiatic Studies and the Journal of Japanese Studies publish the most extensive reviews. Monumenta Nipponica has substantial reviews and is particularly useful for its reviews of books published in Europe often overlooked by other sources.  All 3 journals are available online through JSTOR except for the most recent 2-5 years.  Academic Search Premier will cover recent books reviews, but it does not include Monumenta Nipponica.  Another alternative is to search  Web of Science which includes all 3 journals, but is more cumbersome to search.

Japanese language journals:
Zasshi kiji sakuin indexes book reviews published in scholarly journals.