Goodreads
http://www.goodreads.com/
The website permits individuals to sign up and register books to create their library catalogs and reading lists. Nice interface and ability to share with others.

LibraryThing
LibraryThing is a social cataloging web application for storing and sharing book catalogs and various types of book metadata. It is used by individuals, authors, libraries and publishers. It is a bit more intense than Goodreads especially with its extensive lists and tagging.

Library Booklists read-alike fiction (adult) http://librarybooklists.org/fiction/adult/adultindex.htm
This site collects links to library web pages that provide lists of fiction books on a wide variety of topics and if you likes for adults.  The if you likes section includes lists for general fiction, mysteries, romance and science fiction/fantasy.

Library Booklists read-alike fiction (teen)
http://librarybooklists.org/fiction/ya/yageneral.htm#yaif
This site collects links to library web pages that include if you likes for teens as well as lists of fiction books on a wide variety of subjects of interest to teens.

Anniston Public Library
http://www.anniston.lib.al.us/readalikes.htm#M1
A library webpage with an excellent list of if you likes.

Readalike.org
http://www.readalike.org
Readalike.org includes if you likes for nonfiction and a wide variety of fiction genres too. Some of these, like horror, chick lit, adventure and graphic novels, are not covered as thoroughly or at all on other pages. Also offers some fun booklists.

Rolling Meadows Library
http://www.rmlib.org/Readalikes.htm
A smaller number of if you like lists, but some good ones.

All about romance
http://www.likesbooks.com
The site provides reader reviews, information about new romance novels and author information in addition to romance if you likes.

Whichbook.net
http://www.whichbook.net/
Use the sliders on this unique site to come up with many interesting books that will suit every mood! Highly recommended!

"What Do I Read Next?"
http://www.whatshouldireadnext.com/
This site is simple and fun. Type in a book or author. You will see books by the author appear as you type. Choose one that you have read or sounds interesting. This will then take you to similar authors!

Stop, You’re Killing Me
http://www.stopyourekillingme.com
Contains great lists of mystery books based on occupations, geographic setting, diversity, and historical period.  You can also search for books by author or by main character. Contains award lists, lists of new books, and just a few if you like lists.

Morton Grove Public Library’s Webrary
http://www.webrary.org/rs/flbklistgenre.html
Creative lists of fiction books on a wide variety of topics.

Hennepin County Library’s Bookspace
http://www.hclib.org/pub/bookspace/FindAGoodBook.cfm?Genre=fiction
More creative lists of fiction books on a wide variety of topics.

Rolling Meadow Library
http://www.rmlib.org/Booklists-4.htm
And still more creative lists of fiction books.

WorldHum: The 100 Most Celebrated Travel Books of all Time
http://www.worldhum.com/features/lists/the-100-most-celebrated-travel-books-list-20100427/
A list of classic travel books.

Black Expressions
http://www.blackexpressions.com/
Information on books by African-American authors.

Christian Book
http://www.christianbook.com
Information on Christian fiction.

Fictfact
http://www.ficfact.com
Good website for finding information about series.

Fantastic fiction
http://www.fantasticfiction.co.uk
Offers information about new books, authors, series and awards in the fantasy and science fiction genres.

Book Page
http://www.bookpage.com
Provides information about new books, popular books, blogs, reader reviews and more.