[Online] Dictionaries and Lexicons
Edward William Lane's Arabic-English Lexicon is considered to be by far the most scholarly and comprehensive Arabic-English dictionary available. Originally published in eight volumes with more than 3000 pages, it is now also available online.
Hans Wehr's Arabic English Dictionary: view online and/or download
John Penrice, Dictionary and Glossary of the Koran: In Arabic and English (info), and a substantial part of it is available on Google Books (but not in its entirety). If a reader finds it available for online viewing in complete form, let us know.