I also have the PenFed 5% automatic credit for gas, which was grandfathered from a prior offer where they gave other %'s back on other categories. I thought they now only offer a "points" system, but maybe you can still get the 5% on gas.
I'm not a fan of points; just give me the cash. Preferably monthly, not annually.
I'm surprised no-one mentioned another highly-rated card, the CitiBank Double Cash. Basically 2% back on everything if you pay your full balance on time each month. You can take it as an account credit, although it's not automatic.
I'm going to look into the 5% Amazon deal, that seems great, thanks!