Political cartoons have many uses, particularly in teaching. They provide a quick visual statement, and they also invite discussion, not only of the immediate topic, but of many aspects of the period in which they were drawn. Several collections are on-line, some of which may be searched via relevant keywords such as "business," "railroads," etc. A few websites of interest:
Political Cartoons from the Library of Congress
(The LOC blog also has an essay on teaching with political cartoons: "Seriously Funny," with an excellent link to the term "political cartoon" searched in the Prints and Photographs Division)
American Political Prints, 1766-1876 (HarpWeek at the Library of Congress) (HarpWeek also lists other freely available topics on its website)
Railroad Cartoons (Mark Aldrich, Smith College, with commentary)
Treasury of Fine Art, Political/Editorial Cartoons (Ohio State)
Thomas Nast (Ohio State)
Billy Ireland Cartoon Library and Museum, Ohio State (Digital Albums and Digital Exhibits); they also have a searchable cartoon database.
19th and 20th Century Labor Prints (Southern Labor Archives, Georgia State)
Comic Art at Princeton University (includes images by Hogarth, Gillray, and Cruikshank)
Gillray Collection (Princeton University)
Editorial Cartoons of J. N. "Ding" Darling (Drake University)
Political Cartoons from the New York Public Library Digital Gallery
Modern (1952- ) Canadian Political Cartoons (Simon Fraser University)
