Readymade has a great article about the WPA and the creation of the Federal Art Project, launched by Franklin Roosevelt during the Great Depression. As Steven Heller writes in the introduction "The FAP served a dual purpose: It gave unemployed artists work while demonstratively branding the virtues of the nation through rousing mass communication." Most posters were silkscreened, which explains the lack of photography and the simple typography (I love them all).
The posters promoted all kinds of topics including basic hygiene, tourism, health topics, workplace safety, theater, education, public libraries, and community events. Though I feel a bit bad for the poor fellow who had to do the poster for venereal diseases.
Readymade then asked 5 artists to create a WPA inspired poster for today. My favorite comes from Nick Dewar, an illustrator who always makes me happy with his hand drawn type. (I had the pleasure of working with him once for an article I did at MS Living). You can download a large PDF version of his poster here.
Here are a few of my favorite WPA posters: