• Jim Breen's Japanese Page One of the definitive sites for information on the Japanese language on the web. Jim has been around a long time.
• Japan Cast podcasts.
• Nihongo Resources has dictionaries (e<->j, particles, names, etc.), kanji information, lessons, and various information about Japanese.
• Meguro Language Center downloads has a lot of content for download specific for those studying for the JLPT tests.

Dictionary/Translation

• RomajiDesu WWWJDIC based English <-> Japanese dictionary with audio tts, examples, kanji lookup, etc.
• Japanese dictionary Lookup words, kanji characters, kanji combinations, convertor between Romaji and Kana, view kanji in example sentences
• jeKai An open, free, online Japanese-English dictionary. Somewhat small number of entries, but contains extensive information on usage, etc., of what it does have
• Jim Breen's WWWJDIC Excellent Japanese<->English dictionary, with examples of use, grammar information, kanji lookup, etc.

• Eijiro on the web Searchable version of the Eijiro J<->E corpus/dictionary.
• unnamed corpus Searchable J<->E corpus
• Jedo J<->E Dictionary with an emphasis on medical terms
• Infoseek Multi-Dictionary J<->E, kokugo, and katakana dictionaries
• JE-Dictionary online Japanese-English dictionary.

• Jeffrey's Japanese<->English Dictionary

Online learning

• Collin's Japanese Language & Culture Page Great source for links, notes on self-study, etc.
• Learn to Speak Japanese Online Learn Japanese for free.
• Japanese guide to Japanese grammar, A Grammatical explanations for thinking in Japanese
• Meguro Language Center Lots of downloadable material
• MIT OpenCourseWare Offers some Japanese course material
• Pera Pera Penguin´s 5 Minute Japanese Classes Yomiuri´s nice lessons
• Teach Yourself Japanese TAKASUGI Shinji's good set of lessons

Online quizzes and tests

• 文法クイズ
• Japanese-Language Proficiency Test Test Japanese grammar and vocabulary for free.

Sort

• WaKan Project
• kantango.com
• moji.mozdev.org
• rikaichan
• yoshida institute