I'll throw out another option that worked well for me (and also, I think, for my cofounder): Academic CS research. I tried this the summer of my sophomore year

I'll throw out another option that worked well for me (and also, I think, for my cofounder): Academic CS research. I tried this the summer of my sophomore year and it was an excellent way to develop my (already ok) scripting/hacking skills. Methodologically, it was a bit of a mix between internship and self-study. You would likely have a large amount of time in which to indulge/engage your particular interests, but you would also have some semblance of direction (i.e. the research project). I ended the summer having learned lisp, built a number of frameworks (not all of which related to the research), bettered my scripting skills, and written a paper (which we published). I didn't make a lot of money, but otherwise it was a pretty good deal.