MapQuest
Leading online mapper - offers turn-by-turn trip directions.

Rand McNally
Leading print mapmaker provides clean zoomable maps online.

FreeTrip
Can show hotels, restaurants and average fuel prices along your route.

Roadside America
Quirky attractions - the site is a great ride in itself, even if you're not planning to hit the road.

Road Trip USA
Maps out 11 road-trip routes across the US, listing attractions, diners, festivals, radio stations, and more.