This is an essential cumulative overview of American Bestsellers for much of the 20th century. It is engagingly written, well organized, and well documented, with cumulative sales figures you can't get anywhere else, which is why this edition is on reserve.
Wikipedia is a fine place to start, but this entry (like many others) is uneven in quality. The sections on Descriptions and Types of Bestsellers is pretty good; the section on Early Bestsellers is pretty bad. Caveat Lector.