The Bill & Melinda Gates Foundation has adopted an open access policy.
Here's an excerpt:
As of January 1, 2015 our Open Access policy will be effective for all new agreements. During a two-year transition period, publishers will be permitted to apply up to a 12 month embargo period on the accessibility of the publication and its underlying data sets. This embargo period will no longer be allowed after January 1, 2017.
Digital Scholarship | "A Quarter-Century as an Open Access Publisher"
