Design is History, a great overview on centuries of design. Part of the graduate thesis of designer Dominic Flask, Design is History was created as a teaching tool for young designers just beginning to explore graphic design and as a reference tool for all designers. It is supposed to provide brief overviews of a wide range of topics rather than an in-depth study of only a few. It is a constantly evolving, changing, expanding reference library.
I am about to send some serious time with this website. You should too.