Archives go back only to 1996 at this time. New York Times Book Review - Archives of reviews back to 1980. Includes links to many first chapters. The Romance Reader - Three thousand reviews of contemporary romance. New reviews are categorized by subgenre.
Nonfiction is arranged by subject.
Archives are available with a paid subscription. BookBrowser - An excellent website for fiction Reader's Advisory material. There are also thousands of reviews of current fiction and lists of forthcoming titles and bestsellers. The author section includes interviews, links to author pages, pseudonyms, events and signings. Links to online book discussion groups too.