Sarah, This is an area that is really gathering steam. Did you see the article in the Fall 2008 edition of Digital Directions magazine? (www.digitaldirections.org). There are several related pieces there. If you can't find it online, let me know and I will send you mine.
I would also point you to the National Repository of Online Courses (NROC). Here's their website: http://www.montereyinstitute.org/nroc/
I'm also at the front end of a project where we are designing a very 21st century virtual "course" that will have a very open architecture and lots and lots of content for students to choose. It's a physics course and being developed with backing from NASA. Happy to tell you more about it and related project (the Virtual Learning Magnet) which we are developing under the auspices of CCSSO, the Council of Chief State School Officers.