Finding published book reviews from reliable sources can be a challenge in the online environment. The databases here can help you find good reviews published in established, credible sources.
New York Review of Books - selected reviews
New York Times on the Web Books - Books and authors from reviews, news, and interviews in the New York Times back to 1981.
Quarterly Black Review - focusing on books of interest to African-Americans
Washington Post Book World - Washington Post Sunday book review section
H-Net Reviews - very current reviews from the Humanities and Social Sciences Online Network (free source)
Literary Criticism - from the Internet Public Library. Contains critical and biographical websites about authors and their works that can be browsed by author, by title, or by nationality and literary period.