As a teacher, I’ve always operated on the assumption that students are primarily interested in each other. Here’s a fun activity that takes advantage of that interest to teach students a little about data visualization. It’s an extremely unscientific Cosmo-style quiz, designed to show students which interests they have in common with each other. It’s just an introductory lesson, but it gives you a fun dataset to play with. You’ll probably want to split this among a few class sessions, since students will need at least one full class to just get familiar with Gephi.
Of course, it’s also a good chance to talk about how authoritative graphs like these can look, and whether the data these contain actually means much at all. (Probably not!)