For the iPhone/iPad users out there, I've been using several apps that have been really helpful, in addition to workbooks and software.

iKanji touch - if you're at a level where you are starting to learn kanji, this is a GREAT way to learn and practice. It not only teaches kanji meanings and their readings, but also the proper way to write them.

Human Japanese - this is available for PC as well and takes you through the basics, teaching hiragana then katakana, then on to grammar, etc. The text is full of cultural references as well, which I found very educational.

Kana Flip, Japanese Flip, Kanji Flip - Flashcards on the go basically, also found it very useful for practice.

On another note, there are sites online to practice Japanese with native speakers (I'm deleting the name of the site, as apparently it's against the rules. Sorry!). I haven't used it extensively yet so I can't be definitive in my opinion here, but it allows you to interact with native Japanese speakers. It's a site where you might teach someone a bit of English (or any other language you are fluent in) while they help you with whatever language you are interested in.

I hope these are helpful!!