I'd like to add two things to this discussion:
1. Request these early, like at least a few weeks before you need them. You'll feel really stupid if your application was finished by Halloween, but you don't go complete until after New Years (like me).
2. Several schools also require a Dean's Certificate for disciplinary actions, which I didn't anticipate. In my experience it was Columbia, NYU, Duke, and USC. There are probably others.
Sorry if I'm repeating other people, but this was the major delay in my application process and I think it's really important to think about.