I say flashcards and work books. Flash cards especially.
They are easy to take with you and it's very easy to look at them, turn them over and see the meaning. After enough practice you will be able to look at them without turning to see what they mean.
Work books are to learn how to write them. I have the JAPANESE From Zero! 3 book which is from yesjapan.com and I am planning on getting the rest of the books when I have the money for it.
This book in particular is about kanji and writing it. This is a progressive series so you should get them all if you intend to buy them. I bought number 3 as a test to see what it was about and if I felt it would help me and discovered that I needed to know how to read the kana's in order to read the book.
A very great series, you should take a look at it man.
Of course you don't need all this, you can use the link Jura gave you :]
I like to have a book in front on me and something to hold on to though, as it gives me the "I am now studying" feeling, rather than sitting on my computer oogling at a website. There are also many flashcards apps for smartphones such as the iPhone and Android platforms.