There's plenty of sites out there that offer D&D campaign maps. Most of 'em suck. You totally lose the feel of the story you're telling if you hand the players something that looks like it was made in Mspaint on an EGA montior. And I mean I could draw something, but it'd obviously look like, well, I drew it. And my drawing skills lie more in the realm of funny comics than cartography. So I figured why not base a campaign and its stories on actual places?
Behold the glory that is Google Maps and Google Earth. All this stuff is just ripe for the taking. This, for example, is the overland map that my four players are currently trudging [and sailing] though.
The main benefit of Google Maps is the scalability of the maps. If everyone, for example, docks at an island, I can give an overview of what the island looks like. The players' imaginations fill in the blanks in scenery by taking what they see and turning it into setting. This particular island is on the SW corner of the main northern continent.
This island, considerably harder to see on the main map, lies south of the main island in the upper left on the overland map.
And to those that miss the "Ye Olde" feel of maps: that's what photoshop filters are for.