www.thejapanesepage.com - This is a great website, with a large community dedicated to learning and sharing the japanese language. It also has an online store for purchasing books and other learning materials.

www.jbrute.com/joomla/ - An online japanese-english dictionary. I believe it can also be installed as a windows program. I do not have much experience using it, but it may be helpful to you.

http://jgram.org - A site that depends on community contribution, with a focus on grammar.

http://infohost.nmt.edu/~armiller/japanese/kanjifreq.htm - A list of kanji in order of most frequently used to least frequently used, in Japanese newspapers. It seems to be a few years old, but if you want to study kanji by frequency, it's a good list to start from.

http://www.guidetojapanese.org - A thorough, if sometimes difficult to understand site that is all about japanese grammar and its complexities. I do recommend reading it, but take it slow. It can jump around a lot and there is a great deal of information to soak in.

http://repose.cx/anki/index.html - This is a flash card program and it comes with some japanese flash card packages for free. I checked it out and it's a very neat program. I recommend looking at this one. It is available for windows, mac OSX and linux.