There are many courses at different levels which you can use to learn on-line for free. The contents are presented quite nicely, memorizing the new words is easy as they appear many times in the lessons.
But the really interesting thing is that anyone can create new courses, for example you can find music videos where they teach you the words in the lyrics.
Just go to http://www.iknow.co.jp/ and choose "English Courses" from the "Courses" menu. Create a user account so you can keep track of your progress.