I am a huge proponent for OER. The benefits to the student are tremendous: at the very best, free text books; the very worst, minimal additional costs to take a course.
I have been experimenting with two texts, one for College Algebra and another for Calculus III. In each instance, I have been able to offer a freely available text to my students and modify said text in ways to better serve my students. Such activities are funded by the Auraria Library in the form of a stipend.
Specifically, I have modified APEX Calculus III V4 to include supplemental material for my students in Calculus III. Students report like being able to read a simple PDF and annotate the text as they see fit. I have also offered to my students the chance to submit their critiques of the modified text so as to improve the text for future classes. For College Algebra, I have been using College Algebra 3rd Edition by Carl Stitz and Jeff Zeager. I have thoroughly enjoyed this text and recommend both to whomever is teaching College Algebra or any course in the Calculus sequence. That said, some students do report that the text by Stitz and Zeager is a bit wordy at times. I can see their point, but I believe this is what makes the book more accessible. At some point, I will perhaps blog about my experiences with these texts.
I am also in the process of developing my own videos on background material for various classes.