American Express. Don't leave home without it.
It has the singular virtue of having to be paid IN FULL every month. Hurts like hell some months, but worth it. There is an annual fee, but usually trivial compared to years of built-up interest.
I do have a Visa card for those few places that won't take American Express (Fry's Electronics for one, and my auto mechanics). Of course the key to the Visa card is paying it off every month too, but it's easier to sluff off on it when you have a choice.