SPARC provides a community resource summarizing current federal agency public access policies for both data and articles.  You can select up to three agencies and compare their policies.

On Feb. 22, 2013 the White House Office of Science and Technology Policy (OSTP) released a memo titled, "Increasing Access to the Results of Federally Funded Scientific Research (PDF)." In short, the memo:

"...directed Federal agencies with more than $100M in R&D expenditures to develop plans to make the published results of federally funded research freely available to the public within one year of publication and requiring researchers to better account for and manage the digital data resulting from federally funded scientific research." Michael Stebbins, Assistant Director for Biotechnology at OSTP. 

Links to how each of the agencies chose to implement of Public Access Programs in Federal Agencies can be found in science.gov

It is because of this memorandum that many federal agencies require data management plans. A data management plan should always address plans for making datasets publicly available (or, if they cannot be made publicly available, why). Data management plans should also talk about how the data will be managed to keep it safe and valuable.