If you drive a lot, you can't help notice the price of gas.

Track regional gas prices on http://www.DetroitGasPrices.com . The saved search I use is for Ann Arbor prices - http://www.annarborgasprices.com/ . These are from Gas Buddy.

Motor Trend magazine also has a price tracker at http://www.motortrend.com/gas_prices/34/gas_results.html?zip=48104 - they pull their data from fleet credit card purchase information, so it's not subject to human error (but also is only updated 1x/day).

At one point they showed a $0.20 difference between the low price ($2.699 at Packard Street at Carpenter Road and the high price ($2.899 at a variety a places including Packard Street at Stadium Boulevard.