I've recently found 2 useful online resources for learning Japanese. First up for those Kanji-loving people is SPEEDANKI, a site which has an interactive flashcard system which lets you choose what you want to see, what level JLPT you want to learn etc.. You can also register for a free account which then memories the cards you've read and those you havent.
Next up is a reading and listening programme, called NIHONGO JUKU. Various short articles can be both read and listened to at the same time or separately, with a useful vocabulary list below each article displaying any unknown kanji, etc. Its for intermediate - advanced learners of Japanese. A nice site, although it doesnt look as though its updated all that often, maybe one new article every 2-3 weeks.