Of all the prices that folks tend to watch closely, few top the price of gasoline. Here are a couple of resources that can help you follow the price of petrol...
Map of the Oil Balance -- the Export-Import difference.
The US Energy Information Administration gives a short explanation of some of the factors that contribute to the cost of gasoline: http://www.eia.gov/energyexplained/index.cfm?page=gasoline_factors_affecting_prices
Pie Town, NM by Russell Lee.
One of the more useful sources floating about the world wide web is certainly the Gasbuddy.com USA National Gas Price Heat Map, which you can find here:
This map shows you current average gas prices across the country, broken down by county. Zoom the map into a moral local area and county averages shift to zip code averages, and, finally, to individual gas station prices! I have found it generally up-to-date and reliable!
Canadians, fear not, the same Gasbuddy website also has a Canada National Gas Price Heat map here: