Thanks to everyone for their wealth of suggestions. I already had my students playing with turtle. And I had asked them to alphabetize a string (without having previously revealed the sorted() function).
So far, I have taken up the suggestion of the number-guessing game. One of my students has a working version. The logic is a bit clumsy, but it's a fine first attempt. I will also take up the Twenty Questions idea. My son and I played that game a lot over the years, to pass the time on long car rides. And it would be a great way to introduce the binary tree data structure. Another project I thought of was a Pig Latin translator. (But do kids today even know what Pig Latin is? Am I showing my age?) Concerning more advanced, real-time, game-oriented graphics, I am trying to figure out how to build PyGame on top of Python3.x. Supposedly it is possible. I just haven't figured out how. It's 2013: I refuse to complicate my students' programming education with Python 2.x. I used wxPython happily for years, and I think that its graphical capabilities would probably be up to the task of a simple 2D game. Unfortunately, it has the same problem as PyGame, at least for now. The Py3-compatible version of wxPython, to be known as Phoenix, is still under development. I'll keep Unity, Panda3D, and Blender in mind for later. Again, one of my main concerns will be Python 3.x compatibility. -- http://mail.python.org/mailman/listinfo/python-list
