Here are the two principle sources for up-to-date gas prices in your immediate vicinity. Indispensable tools for the daily commuter:

http://www.gasbuddy.com/
The best known and, generally speaking, most reliable of gas price listings. Searchable by state and zip code. The only caveat is that prices are usually posted by the gas stations themselves, so some prices are “membership prices” and the like. Especially helpful is the map, easily navigable and showing the location of gas stations with their relative prices.

http://www.automotive.com/gas-prices
Another site, also searchable by state and zip code. Unfortunately this might be lagging a day or so in prices, which sometimes can make quite a bit of difference. No map available.