American Express. Don't leave home without it.
I've had one almost since I was out of college, and use it everywhere except a small number of places (like my mechanic) who only take Visa.
You HAVE to pay the whole bill every month, and while it made me squeal like a piggy in some bad months, the balance never accumulates.
Sure, you can pay the whole balance on any card every month (and it's a good idea, although the card companies hate you for it), but when I was 20, I was realistic enough about the temptation to like the idea of not having a choice.