Shadowing
I'd recommend getting this book, or at least carefully reading the explanation on the site. This technique will significantly improve your pronunciation, and help your conversations flow, as well as drilling in vocabulary, grammar, and whatever else you choose to use as material. Just try 10 minutes a day with one set of material for a few weeks at a time.
A Dictionary of Basic Japanese Grammar by Seiichi Makino
This is something of a standard reference on Japanese grammar. The information in this text can answer just about every grammar question at this level I've seen asked on this forum. Everytime I see one of these questions, it makes me wonder why every Japanese teacher doesn't recommend it to their students. It has two follow up volumes that you'll also find indispensable. I'd have a hard time getting by without them.
Remembering the Kanji by James W. Heisig
This book is one of the two things you'll need to master kanji faster than you ever thought possible. It teaches you kanji with a structured approach that starts you off mastering simple characters and radicals that feature in more complicated characters, which are a breeze when you get to them. The main idea behind the book is its mnemonic system, though, which works shockingly well.
Read some of the reviews on Amazon for some success stories, but ignore the people who say "it's no good because it doesn't teach you readings", because these people are using techniques that outdate the characters themselves, and missed the point of the book more than McCain on the economy.
Anki
If you've never heard of SRS, it stands for Spaced Recognition System, and is surprisingly simple, yet clinically effective. Basically, you review a Flashcard, and the scheduled time that you will next see that card changes depending on how well you remembered it. This is the best way to test your memory; you'll wonder how you ever learned anything without it.
You can start using it straight away by adding vocabulary you want to memorise, which is what a lot of people use it for. However, it has limitations with words that can't be easily translated, and it's instead much more effective to add
sentences containing the word you want to learn in context.
Once you finish Heisig, this method, commonly called sentence mining, becomes the second thing you need to learn kanji faster than you ever thought possible. You start off by pulling out sentences from news articles, websites, example sentences in your grammar dictionary, Jpod lessons, etc, which have kanji and vocabulary that you can't read. Then you add definitions of the words you don't know, and Anki generates the kanji readings, which go on the answer side of the Flashcard. Here's an example from my deck:
There's more information on
this page.