Tae Kim's guide is good: http://www.guidetojapanese.org/learn/
If you're looking for books, Routledge's Modern Japanese Grammar is very thorough. "Using Japanese: A guide to Contemporary Usage" by William McClure is good for getting to grips with the nuances of some more advanced stuff.
On the more beginner side, I really liked Oxford's Japanese Grammar & Verbs, small enough that you can read it cover to cover easily but it hits all the main points. I also liked the Practice Makes Perfect series for drills.
And if you're serious about it, the Japan Times' "A Dictionary of [Beginners's/Intermediate/Advanced] Japanese" (they are three books) is probably one of the best resources there is for Japanese.