The Islamic Law section of Religious Legal Systems: A Brief Guide to Research and Its Role in Comparative Law by Marylin Johnson Raisch discusses the basic sources of Islamic law and links to online resources.
Links to other Islamic legal research guides were posted by David P. Dillard on a Temple university listserv.
The International Islamic University Malaysia posts a searchable Research Gateway containing Islam-related documents and videos. See also their Digital Library and Library Catalog.
The Index Islamicus indexes articles on Islam and Islamic culture.