In "Institute of Education Sciences Has an Open Access Policy," Stuart Shieber reports that the U.S Department of Education's Institute of Education Sciences has an open access policy.
Here's an excerpt from a recent EIES grant announcement, which was listed in the Federal Register on March 23, 2009:
Recipients of awards are expected to publish or otherwise make publicly available the results of the work supported through this program. Institute-funded investigators should submit final, peer-reviewed manuscripts resulting from research supported in whole or in part by the Institute to the Educational Resources Information Center (ERIC, http://eric.ed.gov) upon acceptance for publication. An author's final manuscript is defined as the final version accepted for journal publication, and includes all graphics and supplemental materials that are associated with the article. The Institute will make the manuscript available to the public through ERIC no later than 12 months after the official date of publication. Institutions and investigators are responsible for ensuring that any publishing or copyright agreements concerning submitted articles fully comply with this requirement.