When I think of academic publishing, Oxford UP, Cambridge UP, Harvard UP, Princeton UP, Yale UP and Stanford UP come immediately to my mind.
However, there are many other university presses with over 130 members in the Assocication of American University Press. http://www.aaupnet.org/aaup-members/membership-list
I've found the guidelines for submission to be rather interesting.
Intended for publishing works by serious academics who burn the midnight oil for ten years writing a monograph http://en.wikipedia.org/wiki/Monograph , the primary objective of academic presses is not that of making a profit but creating cultural capital destined for preservation by libraries considered to be citadels for knowledge and, as such, published works are necessarily scholarly works built on research that is not just time-consuming but rigorous.
Recently, William Chace http://press.princeton.edu/titles/8245.html spoke at an academic conference saying that the standard for quality required for academic publishing is such that only a fraction of the submissions are accepted for publication. Some 120-200 books published each year by a university press come with the guarantee that they were peer-reviewed by several experts in the field and authenticated to be genuine works of rigorous scholarship. Many of these books only sell about 200 copies.
University presses may occasionally publish coffee table books that generate profit and compensate for expenses incurred in publishing less marketable books that are worth preserving.
Self-publishing may be on the rise but this is an unlikely option for scholarly works that require critical peer-reviews in order to be taken seriously. As such, self-publishing would be a remote possibility reserved only for those with firmly established reputation in the field.