Free Internet Resources

Doing Business Law Library
The World Bank's open-access law library to business laws and regulations around the world.
International Tax Laws by Country
Portal contains links to the tax websites of about 25 foreign jurisdictions, from Australia to the United Kingdom. There are also links to international tax resources, foreign and international tax associations, and other foreign and international tax websites.
Model Double Taxation Convention between Developed and Developing Countries
United Nations (2001) - UES; STA/ESA/PAD/SER.E/21 (pdf, 2001).
Office of Tax Policy: Tax Treaty Documents
Includes the 1996 United States Model Income Tax Convention, Treasury testimony, and proposed treaties (treaty text accessed from this site is usually proposed text)
Organisation for Economic Co-operation and Development: Center for Tax Policy and Administration (OECD)
Find the OECD’s 2008 Model Tax Convention (pdf), 2005 Model Tax Convention (pdf), other Publications and Documents, and a plethora of information related to international tax issues
Research Guide on International Tax Law
"This research guide, based on International Tax Law: A Legal Research Guide (Buffalo: Hein, 2011) by Christopher C. Dykes, is designed to provide a starting point for those interested in international tax research. This guide will focus on international tax law from the global perspective, but will also list information and sources for those interested in U.S. international taxation. This research guide will also discuss model income tax conventions, tax treaties, customary international law, and general principles of law. Secondary sources such as selected treatises, practice guides, and journals as well as online sources and research guides will also be covered." - from the guide's introduction
Tax and Accounting Sites Directory
Links to tax websites of over 80 countries and all 50 of the United States; links to international resources, IRS information, tax treaties, EU websites, VAT (Value-added Tax) information, and more.
Treaties in Force (TIF)
Office of the Legal Advisor, U.S. Department of State, Treaty Affairs Staff. This publication lists bilateral and multilateral treaties and other international agreements of the United States on record in the Department of State as being in force as of January 1 of the specified year. This is an excellent resource to verify that the treaty you located in another resource is still in force in the United States.
Uncle Fed
Open access website contains bilateral treaties between the U.S. and foreign jurisdictions (in pdf).