General Nonfiction Booklists

Bookmarks Magazine — A wonderful publication that reviews and rates hundreds of titles six times a year.
BookBrowse — Free for the most part, although membership provides access to more in-depth reviews, more search capabilities, an online magazine, a Personal Reading List, etc. Free access includes a summary for each title, as well as its reviews, themes, an excerpt, reader reviews, readers' rating, author biography, and read-alikes. Books can be searched by keyword as well as genre, setting, time period, themes, and award winners. Includes titles for the following nonfiction genres:
BookPage — A monthly book review publication that publishes its print content on the Website. Reviews can be browsed by genre. Nonfiction genres include:

Free Book Notes — "Free book notes, study guides, book summaries, chapter summaries, and analyses ... for thousands of books, plays, and poems," including SparkNotes, Cliff's Notes, BookRags, Shmoop, Pink Monkey, and WikiSummaries.
Goodreads — The largest of several social sites for readers. Searching for a title will typically yield dozens or even hundreds of reviews and ratings as well as a brief description of the book. Reviews can be filtered based on the user ratings as well, so that you can read only reviews by people who loved or hated the book.
iread — This wiki for Iowa librarians includes Adult Nonfiction and Teen Nonfiction. Most lists provide just author and title, but some include brief comments. Some of the genres include:
LibraryThing — Sometimes called "Facebook for books," LibraryThing allows individuals to catalog their own books and then allows users to search those books for lists of similar books as well as user reviews and recommendations. Characters, places, awards, related movies, and tags are also provided for each title.
What Should I Read Next — Given the title of a book, this search engine will generate a list of similar books. Unfortunately, only author and title are provided. There are no reviews or annotations for the recommended titles.

Print Resources

Autobiographies, Biographies, and Memoirs

Humor

"Nonfiction That Reads Like Fiction"

Travel

True Crime