For more information on the history of scholarly publishing and how it is changing, see The Scholarly Publication Process from the AUR Library Information Wiki.The official announcement is on the homepage of the American Historical Society. Many people feel that open access publishing is unsustainable, but others feel that it is the unstoppable wave of the future. The announcement makes these problems clear.
Anyway, HOW DO I FIND THESE MATERIALS?
There is a list available from the AHA, but I have discovered that they are also findable through WorldCat, by searching "gutenberg-e.org" as a keyword. Currently, there are only 52 titles, but they are on all different topics, from art to culture to radium. Click on the link that says
Web Resources: gutenberg-e.org
There will probably be easier ways to find these materials in the future. They are supposed to be included in the Humanities E-Book project (AUR has a subscription), but they don't seem to be there yet.
AUR is making its own attempts at open access publishing and we hope to make an announcement soon.