I'm always on the look-out for Japanese learning links. If you have any worth using, please let me know and I'll add them here.
Rikaichan is an add-on that you can plug into Firefox that lets you choose to display pop-up translations from a dictionary when you browse websites.
Portal for interactive Japanese learning mailing lists. You can ask questions of the mailing list members, but the volume of replies may get tedious to wade through after a while.
This is another "life in Japan" blog that covers all kinds of topics, which may or may not include learning Japanese at any given moment.
Not one of the better learning tools (I can't stand the native-English speakers there; and the PDF's containing the lesson dialogs cost money and are often filled with spelling or grammatical errors) but it's the only long-running "learning Japanese" podcast I've been able to find. I'd love to find at least one competing podcast, but that hasn't happened so far. So, for the moment, this is the best "conversational Japanese" podcast around.
Tae Kim's Learning Japanese Guide
This is a hard text to work with, since it's 250 or so pages long, and I can't justify printing it out just so I can read it at a coffee shop. But it's also clean, logical, and one of the more approachable methods for learning kanji and written Japanese grammar. The home page is here.
Pera Pera Penguin
This is the Daily Yomiuri newspaper's once-every-8 weeks column describing various elements of conversational Japanese, including slang and idioms. (Note, the series has ended, but the .pdf files are still archived on the Yomiuri site.
Another once-every-8 weeks column, this one from the Japan Times, that features different kinds of kanji, their meanings and examples of words that use them. The Dec. 16, 2008, column focused on the negating kanji, mi, fu, mu and hi (未, 不, 無, 非).