Here is the collection of rare book resource links.

Abebooks.com
A resource for locating used, rare, and hard-to-find books online.

Alibris
A resource for locating used, rare, and hard-to-find books online.

Antiquarian Booksellers Association
An organization of booksellers in the rare books industry.

BookFinder.com
A book shopping search engine that scans bookseller databases to find new, used, rare, and out of print books.

Ebay Books
eBay has millions of pre-owned books for sale.

Online Auction News
Online auction news headlines to help those collecting and selling rare books keep up-to-date.

TradersTrade.com Insider
A weblog for people who buy, sell and trade online.

Yahoo's rare book collecting links
Yahoo's collection of rare and antique book collecting resources.