I just got the USAir Visa card for the bonus miles...but my primary card is the BankAmericard.
I get 1.5 Worldpoints for every dollar spent. Worldpoints can be redeemed for cash, travel or merchandise. I use this card for everything, and always pay the balance in full, so I never pay interest. In 2008, I redeemed points for a total of $1250. Bank of America is paying me to use their card.