goo online dictionaries: Japanese/Japanese Thesaurus/E-J/J-E/C-J/J-C goo辞書: 国語・類語・英和・和英・中日・日中・他
Infoseek Multi-Dictionary: J-E/E-J/Japanese インフォシークマルチ辞書: 英和・和英辞典、国語辞典、他
Yahoo! Dictionary: Japanese/Japanese Thesaurus/E-J/J-E Yahoo!辞書: 国語・類語・英和・和英
excite Dictionary: E-J/J-E/Japanese/C-J/J-C excite辞書(研究社 online dictionary): 英和・和英・国語・日中・中日
Rikai 理解.com (Japanese to English, English to Japanese): Cut-and-paste and website translation with pop-up dictionary references.
WWWJDIC: Online Japanese Dictionary Service
Bi-directional English-Japanese Dictionary
Eijiro on the Web: E-J/J-E 英辞郎 on the Web (スペースアルク): 英和・和英
BitEx Chinese Dictionary: J-C/C-J
ハイパー漢字検索 (Lets you find meanings and pronunciations of a hard-to-read kanji from its components.)
和製漢字の辞典 (国字辞典; a dictionary of kanji unique to the Japanese language. Non-searchable.)