The state guides developed by authors from the Federal Writers' Project - a WPA group that came to be during the depression - are fascinating snapshots of the country as it was in the early part of the 20th century. They contain quite a lot of history and local stories and can be a wonderful way to compare the regions with how they currently are.
NYPL Digital Gallery provides free and open access to over 700,000 images digitized from the The New York Public Library's vast collections, including illuminated manuscripts, historical maps, vintage posters, rare prints, photographs and more.
New York Public Library document resources are now available from WITHIN VoiceThread. Could be an interesting way to integrate primary sources with VoiceThread collaborations.
Maybe Jan Zanetis of the KC3 ("Kids Creating Community Content") Project would serve as an expert for us. I'm going to write to her. http://kc3.cilc.org