This is a quick search on the topic of open access books.
See this panel on publishing your academic book in 2009 from University Affairs (not strictly speaking about open access).
Trade association: SPARC (Scholarly Publishing and Academic Resources Coalition of the ARL)
It seems this association is moving into exploring models for books or monographs. From its 2011 action plan:
Publisher Partnership & Incubation Program—SPARC will continue to support and promote useful examples of open-access or other innovative publishing initiatives by:
– Collaborating with university presses and scholarly societies, leveraging Raym Crow’s examination of current collaborative publishing projects, recently published guide, and Web-based resource for campus-based publishing partnerships
– Developing an overview of open-access monograph initiatives, focusing on financial sustainability models
– Working with societies, university presses, and other non-profit publishing initiatives to develop case studies highlighting successful alternative publishing models for journals, monographs, and other scholarly communication genres
This leads to Raym Crow‘s activities page at SPARC, probably someone worth contacting for additional information.
Also from SPARC, this early 2010 meeting about open access to scholarly monographs, called
The ebook transition: Collaborations and innovations behind open-access monographs (see series of 15-20 minute videos). See also this pre-announcement page.
Also, it seems that the University of Oregon Libraries, Office of the Provost, funds open access monographs, according to this SPARC report from early 2011.
Foundation: Open Society from the Soros Foundation
See these Google results for open access books (Guide to Business Planning – Open Society Foundations