A complete online version of the Encyclopedia of Chicago has just been launched and it is immense. It’s simple and well-organized, with a nifty little A-Z index feature to navigate through the articles. They have tons of ancient, detailed maps in high resolution with good zoom/ crop tools (see "Bird’s Eye View of Elevated Railroads, Parks & Boulevards, 1910" for example), and intense Special Sections that dive deeper into particular subjects like the labor unrest of the mid-1880’s and why and how Chicago was built on a grid.
Good stuff. via Metafilter.