Picturing History is a site develped by the National Endowment for the Humanities that has a collection of paintings, drawings and sculptures that have a connection to historical events.  The pictures themselves are great, but the are brought into context as you click on a picture.  You get a descrition of the historical event that inspired the artwork as well as a brief bio of the artist.  The thing that sets this site appart from others is it’s amazing interface.  It uses a very well designed flash interface that makes viewing and researching the paintings easy and fun.  It is well worth taking a look.