What to do after college?

My friend is looking for some advice on what he should do after graduating from Harvey Mudd College. Some relevant bits of information about him are that he

  • is not a US citizen, so he’d only be able to stay in the US if he’s working or at a grad school. He’s open to suggestions for other countries.

  • is great at math and computer science, including doing real-world programming

  • wants to help the world

He’s currently looking for a grad school where he could tackle interesting problems with possible high benefits in the future. I’ve made my own suggestions, but I’d like to get a (somewhat) independent set of opinions from the LW community.

So please suggest away!