I was planning to cover digitization projects on this blog, but then I realized that there is a vast amount of free digital content out there that most people don't know about. I'm going to collect 3 or 4 sources for each roundup.
Perry-Castaneda Library Map Collection - This map archive at the University of Texas (Austin) consists of about 11,000 digital maps out of a collection of approximately 250,000. It is a very diverse collection that covers the whole world. You could spend days exploring it and not see everything.
Civil Rights Greensboro - As you can tell from the name, this site is an online portal to information about the people and events that have helped define Greensboro’s history. It covers local civil rights subjects such as desegregation, the historic February 1960 sit-ins at Woolworth’s, race relations, the Black Power movement, and the Greensboro Massacre of 1979. Content on the site includes scanned photographs, audio recordings of first hand accounts, and transcribed oral histories.
Minnesota Reflections - I'm sure this has been around for a while, but it's new to me. The state funded Minnesota Digital Library has a website that combines access to more than 45k images and documents spread among nearly 100 cultural heritage organizations. They say that they update the collection regularly, so it might be worth bookmarking the site.