The lists for 2011 summer seminars and workshops through the Gilder Lehrman and National Endowment for the Humanities have been posted. Each organization offers multiple workshops that vary in length. These workshops are not fully funded, but offer stipends to offset travel costs.
Gilder Lehrman offers week long workships at various universities throughout the United States and the UK. Applications and a seminar list can be found online and must be submitted by February 1, 2011. Gilder Lehrman covers the beginnings of American history through the present.
NEH offers a couple of different summer options. Their summer seminars are 2-6 weeks in length and cover a wide variety of topics. Teachers in grades K-12 are eligible. You can find the list of available seminars as well as application instructions here.
NEH also offers week long Landmarks of American History and Culture workshops. Again they cover a variety of topics. The list of seminars and application information is available here.
NEH applications for both the seminars and Landmarks workshops must be postmarked by March 1, 2011. Good luck!