All Free Dictionaries Project
Online project to build free translating dictionaries (e.g. English to Spanish) by allowing individuals to add and correct entries. Several dozen languages represented so far. Dictionaries can be searched online or downloaded. Includes links to other free dictionary sites.
Open-source project to add Arabic-language support to Unix/Linux. Many sub-projects tackling individual areas (such as translating GNOME resources), including one called "Wordlist" which is building a free English to Arabic dictionary. The dictionary is downloadable as it progresses, though I'm not sure what software can use it.
Effel's Arabic Dictionary
Free (but small, around 3000 words 7/2003) Arabic-English dictionary program for Windows. Choose an Arabic stem and it displays words that have that beginning. Program also includes some grammar notes, an alphabet/transliteration guide, and a verb conjugator.
Online dictionary for translating English words into Arabic. May also translate Arabic to English. Site is in Arabic.