Hmm. Resources are a tricky one.
I've been learning Japanese on-off for about 4 years. Although I am REALLY REALLY slack.
But over this time, I have acquired a few books.
Minna no Nihongo.
Japanese for Busy People.
Kanji Power...
but... my opinion is that learning from a book is something which requires alot of disipline. It requires motivation to actually go and open the book. And, with my methods of learning, it is not conducive to advancing my language skills.
There are SO MANY websites out there which can concentrate your skills in certain areas - some are good for Kanji, and some are good for vocabulary.
For example, I use a combination of 2 websites for learning my Kanji.
http://kanji.koohii.com
and
http://www.speedanki.com
These are both good for learning Kanji because they both easily let you review those that you really need help with, but they do so in completely different ways.
The longer that you persist with the two sites, the more they start to overlap in Kanji used. And when this happens I get a real sense of moving my learning forward. Its a great feeling.
So, to summarise, I have spent alot of money on various Nihongo books... but maybe this was a waste of time. Stick to the many Web resources and you'll be fine.