This has been making it around the internet in the last couple weeks, so perhaps everyone has already come across it, but the Smithsonian and a number of other outlets have reported on the fantastic Japanese Animated Film Classics (日本アニメーション映画クラシック) site.
This project, which was recently launched in Japanese and English to celebrate the 100th anniversary of Japanese animated film (the first being created in 1917), brings together all kinds of animated works, from short art films to propaganda pieces.
The films can be explored through a variety of categories and genres or can be navigated by titles or author. The English version of the site is still in progress, but there are subtitles on many of the films and the content is amenable to using Google translate. Give it a spin and see what you find!