RikaiChan

And, while I'm talking about cool Japanese language learning tools, I have got to mention RikaiChan. It is a plug-in for the free web-browser Firefox (which, by the way, is better in most ways than Internet Explorer). Basically, it allows you to point to kanji on pretty much any Japanese language page and get pop-up dictionary definitions and readings. It is very slick and, again, completely free: