The free online lessons
Can't stress they're free enough. These lessons are geared towards the serious learner, there is no cutting corners here. The online lessons teach you Japanese the way it's taught in universities, only for free. This has obvious advantages, as well as disadvantages, but the most important thing is that you can get your learn on.
The site is still in its migratory phase, so not all of the lessons have been ported yet, I will get them online and up to date as soon as possible; for now only lessons 0 through 3 are back up. However, don't let the number fool you - the first four lessons constitute about 2 months of material if you'd be taking classes in Japanese.
You're going to get as much out of these lessons as you put in, so I recommend not just sitting there and reading, write along with it and get that learn on! You may also like to download a copy of the free NR grammar book (a bit over 400 pages) which covers all the topics from the lessons in a nicely topicised manner, so you can look up how the book explains certain concepts, should the lessons leave you curious.