Tax Lien Associates, Inc. 
Offers a variety of services and investment products to U.S. municipalities and investors, including acquisition and brokerage, marketing tax-lien land, portfolio management services and software, and an investment fund.
http://www.taxliens.com/LienSource
Offers subscription lists of property lien sales, in some localities.
http://www.liensource.com
Arizona Property Tax Lien Primer
Information from attorney Mark Manoil about the legal and practical aspects of property tax liens and certificates of purchase as real estate investment. Includes news articles and links to related resources.
http://members.cox.net/manoil/index.htm
POA Properties LLC - Able Tax Sales
Offers information by paid subscription about tax lien certificate and tax deed sales, and how to get started investing in them.
http://www.tax-sale.com/
Tax Lien Certificates Network
Provides resources and information exchange for investors interested in buying and selling tax-defaulted paper. Includes related links; registration required to participate in the network.
http://www.tax-lien-certificates.net/faq.asp
JohnBeck.net
Offers educational materials and seminars on tax-sale investing.
http://www.johnbeck.net/
The Creative Investor Tax Lien Group
FAQ, forum, and e-mail list for discussions about investing in tax liens.
http://www.tcinvestor.com/taxliens.php
Lien Exchange, Inc.
Provides marketplace and other resources for investors interested in buying and selling tax liens and mortgage notes. Subscription required to buy or sell.
http://www.lienexchange.com
