found this site today while looking on teh interwebs. you can search any place in NJ and it'll show you the current price of any grade of gas including diesel in the state. You can also submit a price for a certain station if you drive by one. Its a good way to see whose got the lowest prices around. Its noted that the highest prices by far in the state are at Exxon and Lukoil stations.
http://www.newjerseygasprices.com/index.aspx?fuel=A