A good starting point is:
Marjorie Vai and Kristen Sosulski, Essentials of Online Course Design: A Standards-Based Guide (New York: Routledge, 2011).
The grandaddy of all online teaching resources sites is Merlot, produced by the California State University System. It includes thousands of links to interactive sites, learning exercises, teaching materials, and sample assignments, categorized by subject area.
Recent reflections on online instruction include:
Audrey Heinesen, “Benefits of Teaching Online” Inside Higher Ed
An Emerging Set of Guiding Principles and Practices for the Design and Development of Distance Education. https://educause.edu/ir/library/html/cem/cem99/cem9915.html
Michelle Moravic, “Five Lessons for Online Teaching from Finishing a MOOC”, in the Chronicle of Higher Education’s Professor Hacker series.