Abebooks.com - Online marketplace for used, rare, and out-of-print books.

Addall.com - Book search and price comparison

Alibris - Reliable source for out-of-print, out-of-stock, and rare books.

Amazon.com - Buy books online!

Barnes & Noble - Order books, music, software, magazines online.

Book Sale Finder

Bibliofind - Find antiquarian and out of print books.

Biblio.com: New & Used Textbooks - Your online source for millions of new and used college and high school textbooks.

Bookfinder - A book-shopping search engine.  Finds new, used, rare, and out-of-print books.

eWanted.com - Free Internet want ads.

half.com - by eBay

Powell's Books - An independent bookstore's approach to book news and interviews.

Rarebook.com - Boston Book Company