Be Convinced - an excellent introductory site for learning the basics of the Islamic religion. Simple and easy to understand.

The True Religion - a comprehensive archive of articles addressing common questions and misconceptions about Islam and presenting the authentic Islamic teachings.

Islam Today - a very detailed source with an archive of fatawa (religious rulings) as well as a 'Discover Islam' section consisting of in-depth articles examining various aspects of Islam. Also has a facility for submitting questions.

Islam Online - one of the most comprehensive Islamic sites with news coverage, general articles and Q&A on a variety of topics.

The Islamic Network - Nice collection of articles for those interested in Islam.