Wisely or unwisely, I have volunteered to lead a Greek email study group. Starting this week, we are going to fight our way through Douglas Mastronarde's Introduction to Attic Greek. It's probably the most grammatically rigorous of modern textbooks. Each week students read a unit and complete the exercises. hey e-mail them to me, and with the magic of collation software, I put everybody's answers together.
This method lack interactivity; if feasible, I may try to enhance it at certain points in the syllabus with some online learning, though not sure how that will work with students scattered through a number of time zones.
If anyone would like to join the group, see the page I've constructed at: http://tomroper.typepad.com/tr/mastronarde-introduction-.html