Around Memphis, Exxon usually is one of the cheapest options. Join Upromise to save 1 cent per gallon at Exxon & Mobil stations. Its not a lot, but every bit helps! This is 'stackable' with using the Citi Dividend or Preferred Rewards cards to get 5% back on all gas purchases. Its also stackable with the current speedpass promo mentioned above.
You now have to buy 20+ gallons per month at Exxon & Mobil stations to get a rebate. Here are the details:
https://lty.s.upromise.com/8333.do