Use JSTOR to find reviews of books with an imprint/copyright more than a few years old, and ProjectMUSE to find reviews of books published in the last several years. Please keep in mind that all three of these databases index substantive journal articles in addition to book reviews, so be sure to limit your search to "Reviews" in JSTOR, "Reviews Only" in ProjectMUSE, and "Book Review" in Academic Search Complete.
Book Review Digest is a database dedicated to book reviews. It includes records for about 1.3 million book reviews and 550,000 books. More than 100,000 reviews are available full text. Covers 1983 to the present. Reviews are drawn from both scholarly and general-interest periodicals.
Information from the New Yorks Times Books Section