Online National Diet Library materials

The National Diet Library website's NDL Gallery page gives an overview of its "electronic exhibitions," each highlighting a part of the NDL's extensive collection and featuring (quite) high-res images and (mostly) bilingual explanations. I like the "Portraits of Modern Japanese Historical Figures" a lot, but the other exhibitions are also worth a look.

In a different section of the NDL site, you can also find the NDL's Rare Books database - there is not so much content available yet, but trying some Japan related queries, I got a couple of interesting results.