I use Amex cash-back credit card which reward you 1% of your annual spending above $2000. It's not big money but probably enough to get yourself a little present at Xmas.
I know some gold cards can waive you rental car insurance, the problem is most of these cards have annual fees. I applied a Capital One platium card in hope of waiving this insurance if I need to rent a car, but haven't got a chance to try it out yet. Anyone has more precise info?
Sometimes too many credit cards can affect your ability to get future loans, like housing mortgage or line of credit, as credit card limit is deemed as a unsecured loan by the Credit Bureau.