Emory Douglas Hard-hitting political posters by the Revolutionary Artist of the Black Panther Party
Flyer Design Goodness Contemporary and vintage posters, usually collected by designer, from around the world. [Not currently active, but there’s a great archive]
Gigposters 150,000+ band, concert, and show flyers and posters. This is the motherlode! I have a small collection of posters from my 1980s Seattle days on the site.
Occuprint 1000s of posters of the contemporary Occupy movement from around the world. Wonderfully archived and sourced.
The Harry Ransom Center at UT-Austin 10,000+ classic movie posters
USSR Posters Soviet and Russian propaganda and advertising posters, 1917-91
WPA Posters 1930s-40s New Deal-era public works posters, brilliant and graphic
Wrong Side of the Art Trash, exploitation, Blaxploitation, and other cool, bad movie posters
Adult Film Posters Groovy collection of X-rated movie posters, 1960s-70s, via the CineMasterpieces site.