Stefan Landsberger, a professor of Sinology at Leiden University in the Netherlands, maintains a great collection of Chinese propaganda posters online at http://www.iisg.nl/~landsberger/.
They date from the early days of the People's Republic of China all the way up to current posters for the Beijing Olympics, with informative commentary about the campaigns behind the posters. This is a very interesting way to explore how the Chinese government has popularized various messages over the years. Many of these posters are very striking visually, as well!