If you're burning Jet A, you should be using contract fuel cards, at least the free one's. I am currently enrolled in AvFuel, Airboss and Everest, but plan on adding all of the majors over the next month. I've seen savings anywhere from .10 cents to well over a dollar per gallon. I am most interested in CAA. There is an annual fee but i'm told that within a couple fill up the savings will cover the annual fee plus NBAA membership.
Heres a list though of the majors.
AvFuel
Everest
Mariah Fuels
World Fuel
Colt Fuel
UvAir
C.A.A.
Airboss
I'm sure I am leaving others out, but the list above is a great start.
If you fly a lot expect to save at least 10k if not much more per year. Jet A only though...