The original blog post on cheating has helped generate quite a lot of discussion in the blogosphere on how to design assignments to make plagiarism difficult. Here's a link to a post with several good ideas: http://erictremblay.blogspot.com/2011/07/dont-police-plagiarism-instead-design.html
My favorite: Presentations. Or maybe Projects. (Discussions are a no-brainer. Of course I think you need to include discussions in your online course. Where else are you going to discuss the content with your students. In my mind that is still where a lot of the actual teaching occurs.)
Today I listened to a presentation on student retention given by Kae Novak of Front Range Community College. They are using software like Animoto (www.animoto.com) and Prezi (www.prezi.com) to enliven courses, but are also seeing students begin to use there tools. How about asking students to use Glogster to develop a poster (www.glogster.com)? Or discuss connections with Popplet (www.popplet.com)? Any of these would be difficult to plagiarize.