Japanese to English (and back)
WWWJDIC Monash University’s interface for all EDICT Project dictionary files.
RomajiDesu Online Japanese ⇆ English dictionary. A major part of the database uses data from EDRD Group, Monash University.
Denshi Jisho An easy-to-use and powerful online Japanese dictionary with data from the WWWJDIC project.
Tangorin Free online English-Japanese bidirectional dictionary, based mainly on files provided by The EDRD Group.
Nihongo Resources.com dictionaries JP/EN dictionary based on JMDict.
Monolingual Japanese Dictionaries
Rikaisama A modification of the rikaichan Japanese-English popup dictionary for Firefox that adds many unique features such as audio, EPWING support, frequency information, pitch accent, Anki integration, etc.
GoldenDict Supports the dictionary file formats used by Babylon, StarDict and ABBYY Lingvo.
KanjiTomo OCR Program optimized for kanji and with dictionary lookup, perfect for manga and other kinds of non-selectable Japanese text. Kanji lookup is done by pointing the mouse to any image on screen. Requires Java.