The Library of Congress realy does an amazing job of getting primary resources up on their web. Their American Memory Project is a collection of collections. While you can search and browse across all collections. Each collection is a complete resource in it's own right. Recent additions include: The Irving Fine Collection: Ca. 1900-1990, Emergence of Advertising in America 1850-1920 and Edward S. Curtis's The North American Indian Photographic Images . When you hear about some new, awesome, complete collection of primary sources that has just gone online, chances are it's part of the American Memory Collection. Also check out the digital companions to their physical exhibits, most amazingly their collection of pre WWI color photography from russia. Yes pre-WWI COLOR photography.