This site has many links not duplicated on other sites and with international coverage.
Motion Picture & Television Reading Room Library of Congress This is an excellent guide to purchasing and using video selection tools.
This service provides umbrella licensing to nonprofit groups, businesses, and government organizations for the public performance of home video cassettes and video discs. It has an FAQ section and links to IP resources, agencies, and permissions groups.
This excellent online resource has several areas, a searchable and browseable database is available by distributor's name, type of distribution method (theatrical, documentary, education, performance, etc.), this is an excellent online resource. Links to other distributor and video indexes, including mail order, footage resources, etc.