If you want to buy Japanese study books (big industry in Japan, wonder why?
) I have two not-so-obvious recommendations. The information in the second one, you won't find online.
Fistly, the famous:
Making out in Japanese (ISBN: 4-900737-09-7). It contains Japanese slang and is quite funny to read. It's very easy to comprehend since it's all written in romanji. It's a good gift for anyone remotely interested in Japan (well, not your mom perhaps). Some of the phrases are not useful unless you can carry on the conversation. But it can help you get away from "desu-masu" all the time when you get some Japanese friends. It won't really explain _why_ the phrases are built up like that. Also take care with the dirty slang, a lot of Japanese people didn't even know those.
Later on, after learning your basics, you might wanna look this one up:
A dictionary of Japanese Particles (ISBN: 4-7700-2352-9). It is really what took me above the basic Japanese courses. This one will make you understand why and how to speak casually/formally in Japanese. Note, this might not be for the casual learner, but it is Really good to have if you're serious or you study/live in Japan. You should have some other learning material as well in addition to this one.
It covers many (all?) particles and sentence patterns. In many cases you won't find them in the normal textbooks. You will also understand why some expressions work like they do. If you knew enough nouns/verbs and all the stuff in this book, you'd be better off than many Japanese!
If nothing else, you can find out how to be angry/rude: so you know that guy who is yelling at you is probably a Yakuza
.
Another tip I have is to that if you study seriously: try to learn Kanji from the very beginning! I regret I didn't spend more time on it. My conversational skills are miles above my reading skills. Reading books is a GREAT way to learn a language. I owe most my English fluency to the fact that I almost exclusively read only English fiction books from the age 13 and forward. Nowadays I mix more but no Japanese fiction at all.
Light: Do you want this in it's own thread? I think it might be a good idea too keep it here, to collect as many resources as possible!
I already found a wealth of material that I didn't know existed. As well as the urge to start maintaining the knowledge I already have. Thanks everybody!