This may help some find the lowest price especially when traveling, I think it says its updated at least every 48hrs and if your area prices are not listed you can learn how to be a spotter for them
a color coded chart of prices in the states by county
Gasbuddy Gas Prices
on this page you can also
enter a zipcode and it will give you a local map and price for the stations listed to find the lowest price in any area
Gasbuddy Map Gas Prices - Find the Lowest Gasbuddy Gas Prices on a Map
and one for canada
Canada National Gas Temperature Map
and this one shows the history of change
Historical gas price charts - Gasbuddy Gas Prices