If you only want one card, I probably would not go with an AMEX since its not accepted everywhere.

If you dont mind carrying two cards, the SPG Amex is a great choice.

Depending on your spending habits, you might want to check out the PenFed Visa Cash back card...

5% on gas (regardless of what gas station!)
2% on groceries
1% everything else

Not everyone qualifies as its a credit union and has some stringent requirements, but its a great card.

No annual fee, and the cash back is automatically credited to your account monthly, very hassle-free.