Genki Online Self Study Room: Interactive exercises to accompany the Genki textbook
The Japanese Page: Contains Japanese lessons for beginners, including information on reading and writing hiragana, katakana and kanji
Gahoh: A site for learning to write hiragana, katakana and kanji, with stroke order demonstrated in Quicktime movies
Dictionaries and Reading Aids
Jim Breen's WWWJDIC: Japanese to English online dictionary, paste words or text.
Denshi Jisho: Japanese/English online dictionary for words, kanji and sentences.
Search Engines & Encyclopedias