The absolutely ultimate reference on Japan. Library use only, at US$780 is a bit too expensive to add to your own collection. (TIP: Always check here before starting any essay on anything related to Japan).
A condensed version of the previous title with the same high standards.
Although this contains a lot of information, I think it tries to cover too much in too small a book, and is therefore not useful if you want to know about something in depth, uncharachteristic for an encyclopaedia.
A compact, useful and comprehensive guide.
An older but still useful reference dictionary on Japan.
Published yearly. Good value guide to all the statistics (and more) you'll need on Japan.