Google's EduMOOC is astounding and fun. You can be in touch with 2500 teachers and learners in the grand experiment in volunteer, free, online learning.
Although the MOOC is just for this summer (July-August), you can use the discussions, videos, and resources (Diigo group) asynchronously. Read all about it at Polly Peterson's Education-Portal blog.
Sign in to Google first to access everything.