Rory McGreal, UNESCO/COL Chair in OER at Athabasca University, recently shared that the university press at Athabasca has published the first in a series of open textbooks, available for free download under a Creative Commons license.  From his post on the OER Forum:

AU Press has just published  two course texts in the  OPEL series (Open Paths to Enriched Learning).  These books are teaching focused, and for undergraduate courses. There will be more coming (hopefully a couple a year).  Here are the links to each of the books.

You can also order print copies for a modest fee.  Great to see more open textbooks rolling out!