Arabic Dictionary
Listening Practice for Arabic
Arabic grammar, vocab and reading resource
Cambridge Arabic-English dictionary
Arabic Language Transfer: Language Transfer teaches you to 'think' in the language you are learning to speak.
Arabic Voices
University of Texas website that is designed to help improve the listening comprehension of Arabic learners.
Madinah Arabic
Site providing free Arabic resources and flashcards.
Omniglot
Good beginning guide to Arabic.
Writing Arabic
Yamli
An Arabic search engine that allows you to type in transliterated Latin letters to get the Arabic words for running searches of Arabic websites.
The United States' Foreign Service Institute's old language courses (from the 1960s and 1970s) are available for free online. They are a little old content-wise, but they allow a student to take a free course in Arabic online. This site also has access to the Defense language institute's old courses, which include General Arabic, Iraqi Arabic, Saudi Arabic, Syrian Arabic, and Egyptian Arabic.