smart.fm - Excellent site to learn Japanese

Among the many internet links to good sites about Japanese, Smart.fm is probably the best. This is a site on which you can grow your knowledge of Japanese at your own pace by using the iKnow quiz application (runs in your internet browser).
iKnow is very well made: it remembers which questions you had trouble with and which were easy, and it revisits all questions anyway to make sure that you remember them.
More importantly, it lets you practice different aspects of the language at the same time:

Vocabulary

Every item you learn is about one word.

Kanji

If you set up iKnow to show you kanji, you learn the kanji at the same time.

Grammar

Each word comes with an example sentence, so you learn or rehearse some grammar at the same time, too.

iKnow keeps track of how often you visit, how much you study each time and so on, so it adapts itself to your training schedule.
Their Japanese Core 2000 course, in 10 packages (package 1 is here) gradually builds up your knowledge so that in the end, you know 2000 words. This can take a long time; I'm still doing Step 1 at the moment.
If you have any problems working with this site or the quiz application, let me know. It is brilliant and, best of all, free! Do note that the Web site is sometimes not available.