Cornell, Sean, et al. "Interactive Activities in Online and Hybrid Courses." Science Education Resource Center at Carleton College.
Intended for courses in the geophysical sciences, but provides ideas and examples that may be useful in other disciplines.
Gilman, Todd. "Designing Effective Online Assignments," The Chronicle of Higher Education (22 March 2010).
Short article providing general tips and suggestions for creating online assignments.
Holmes, Ann, et al. "Using Data to Teach Geology in College-Level Online Classes." Science Education Resource Center at Carleton College.
Provides suggestions on using real data in online activities; especially useful in planning assignments for science and social science courses.
Schafly, Theresa. "Resources for Developing Blog and Twitter Assignments." Georgetown University Center for New Designs in Learning and Scholarship.
Provides some thoughts on incorporating social media and related online tools into course work.
Waldrop, M. Mitchell. "Education online: The virtual lab," Nature 499 (18 July 2013).
A brief article on the subject of virtual/remote lab activities. Presents some examples of how to incorporate these into online courses.
"Assignment Design." DePaul University Teaching Commons.
Not written specifically for online courses, but the list of resources for specific types of assignments is helpful in suggesting activities that promote different types of learning (i.e., case studies, fieldwork, writing assignments, critical thinking, etc.).
"Activities for Teaching Online." Science Education Resource Center at Carleton College.
A list of examples, drawn from science courses.