Ask HN: How do you choose your weekend projects?

I've been trying to come up with some kind of personal project for myself to do but quite honestly I'm hitting a wall - kind of like writer's block. I'm a 3rd year CS student so I have some programming experience, but nothing of the "make something from start to finish" kind. I've made small games in 24/48-hour competitions, and small things like a Boggle-solver or Tic-Tac-Toe to get comfortable in a new language, but I'm trying to think of something that's not a game nor a tiny project and that's harder. I know it's a big gap in my education and I want to cover it (I'm excited at the thought of developing something bigger, just having trouble thinking of what).

So, how do you choose what you code on your free time? Do you come up with your own projects? Do you contribute to open-source? Do you just make lots of small things? Or do you not have time for that sort of thing because you're working 24/7? (=P)