I think about this issue a lot since I commute about 150 miles per day, using $300 a month worrth of gas. I live in Michigan.

The best strategy I have found is with Speedway. They have a cobranded credit card that gives a 4% rebate on Speedway purchases. When you buy a Speedway gift card (refillable, any amount) you also get a discount of $2 per $50 spent (another 4% discount.) Once a month, I use the Speedway CC to load up my gift card with $300, which costs me $288. Then I receive a 4% rebate on the $288 ($11.52) for a total price of $276.48 for $300 worth of gas.

Then I use my Speedy Rewards (loyalty) card to add up points. I am about to reach 34,000 points ($3,400, although they have bonuses for stuff like milk so I didn't actually spend that much) which will get me a $50 Speedway gas card.

This is the best I have been able to come up with. However, what I really want is a diesel car (which will apparently have to be a VW) so that I can fill up with biodiesel, thus buffering me from the fluctuations of the petroleum market, creating less environment-destroying pollution, and reducing my personal dependence on oil which results in the US giving money to terrorists. I really want that Jetta.