Write a five-paragraphemail you could send to a person you would like to list as a reference, asking their approval to be contacted by your potential employer. Address it to a specific person, real or not. You'll want to "get in" by referring to how you know or worked with the person as your context. Then, state simply that you're in the job/internship market and you'd like to be able to send potential employers their way to ask about you. Perhaps mention a few of the high points of your performance in his or her employment (or class) to refresh their memory. "Get out" by reminding them to contact you with questions and their OK. Ask them to confirm their preferred contact information, and thank him or her in advance for their assistance. Five paragraphs should be sufficient for this note.