Thanks everyone (well, the 11 people who responded) for your responses to my survey for the last Physics classes of the year (or forever for students not taking Physics next year).
I had 11 responses, 6 of which were related to astronomy (everything from simple astronomy to the 5th dimension and black holes) and one was for practical work (not just using computers), so this is by far the most requested topic.
In fitting with that, one class will be on basic astronomy - the Earth, Moon, Sun system, which is far more complicated (and hopefully interesting) than it first appears, and we will make sundials. The second class will be on astrophysics ideas (not the Math behind it), the big bang, black holes, black holes etc.
Thanks again to everyone who responded!