If you're a Good Sam member, you can get a "Pilot - Flying J" gas credit card, for free (no annual fees either). Card entitles you to I believe 2 or 3 cents off a gallon when you stop for gas at their service stations. I think they give you $1,000 credit on the card, & you can view your monthly statement (or live statement) online. If you're not a Good Sam member, I think it only costs like $20/year, and entitles you to many deals including Camping World & Good Sam campground discounts. Pilot - Flying J website has more details, as well as their thousands of gas bar locations by state.
http://www.goodsamclub.com/ http://www.pilotflyingj.com/