We just opened an account with Fidelity because they give 2% on everything, payable in $50 increments (posted to your Fidelity account).
Costco used to be 3% on restaurants, and the gas maxes out at $3000 spent per year. SO, we are moving away from using Costco.
If you want 5% on gas, look into the Pen Fed Platinum cashback rewards Visa. 1% on everything else and no annual fee. We're looking at this one as our gas card.
We've been doing a lot of credit card shopping lately. There are some very informative sites we've come across in our searches with good info out there.