Ideas for Tiny games for classes.

I've been teaching game development for a while, and tend to focus on 2 types of games for new developers:  a 2D Space shooter, (as seen in my book) and an RPG/MUD style game typically done in windows forms.

While they cover the basics of programming/OOP pretty well, I'd love to get some fresh ideas in the class room.  I teach on a variety of languages, engines and platforms, so this is mostly a question of genre and key playable features.

I'd really love to hear what you think might be a great game to use for teaching game development.

OR, perhaps a method to build a game.  I tend to have the students create a descriptor engine for the 2D shooter, so they can easily apply physics, AI and other characteristics they want to which ever game object they want, while still learning a lot about Inheritance, overriding and other special features.  (as seen in my book)

Thanks!  :)