WWWJDIC
WWWJDIC is an free online dictionary developed primarily by Jim Breen of Monash University in Australia. WWWJDIC makes use of the electronic JMDict/EDICT dictionaries as well as KANJIDIC to allow for various forms of word lookup, text translation, kanji lookup via various methods (Multi-radical, stroke count, etc.) and has become an indispensable tool for researchers and students of Japanese around the world.
The iPhone frontend was developed primarily to quickly input kanji for easy lookup while reading texts. The traditional Chinese input method allows for stroke recognition by simply drawing characters with your finger. This frontend provides a user-friendly interface - which Japanese languages students of any level will enjoy.
WWWJDIC has similar functionality to other electronic Japanese dictionaries, but is being offered at no cost.
NOTE: I have received many requests for offline functionality. However, this would require a major overhaul of the program, taking time and effort that are not readily available at the moment. Thus, at this time, there is no plan to make the dictionaries available offline. Sorry for any inconvenience this decision may cause.
UPDATE: Many have reported problems of crashing during kanji lookup. This is due to a change on the part of the WWWJDIC website which is throwing off the frontend's ability to interpret its output. The issue has been addressed and an update has already been submitted to Apple.
