Since my last diesel fill up was over $200, I'm looking to save whatever I can on fuel.  Has anyone got any tips or suggestions on fuel discounts, clubs, rewards, etc?  I know a lot of places have some kind of incentive program, but I'm finding a lot of them have all sorts of fees or only discount when using thier credit card.  I'm definately not looking for more credit cards or to get "tied" to one company if I can help it.  Any ideas on ways to save at the pumps?

We use a rewards credit card that gives us 3% cash back on all gas purchases (but with a cap of $12/mo, then it reverts to 1%).  

 A lot of RVers seem to plan their routing around Costco's/Sam's discount pumps... but in my experience, they don't offer diesel very often. 

 We also use GasBuddy on our iPhones to locate the best prices on fuel. Especially with diesel, prices can fluctuate wildly. We've seen up to .50 per gallon differences within stations just a mile apart from each other.