AAA has made its previously members-only TripTik technology available for general use online. In addition to the mapping and directions tool, which isn't much different than what you'd get on Mapquest or Google Maps, you can also use TripTik to zoom in and find the locations of and basic information about accommodations, attractions, and gas stations. It looks like it's possible to check gas prices at some locations as well.
This is the sort of thing I always wish for when I'm already on the road. Were I a little more technologically advanced (and willing to pay for the privilege) and used phone-based internet, it looks like I'd eat well and never overpay for gas.