Google Maps - Quick and easy to use service with customizable maps, aerial and street views. Uploads faster than many of the competitors and is always making improvements. This makes scouting a breeze. To read more check out this review by BasserDrew.
Maps.live.com – Aside from the traditional aerial and street map views, a special birdseye view makes this site unique for river bassers. This site may upload faster than any of the other mapping sites and seems to be getting better by the month as well. Check out my review for more information.
Maptech Mapserver – This is the best site I have found for online topographical maps. It will show shoals in a river if they are significant and even has the names of rapids, islands and obscure land features.
Yahoo Maps – Similar to Google, but without all the bells and whistles. Sometimes you might want to try several services to try and get a better picture of the river or creek you are scouting. Yahoo is worth using to possible get a better view.
Terraserver – TerraServer has been around for a while but hasn’t progressed like some of the other sites. They still use watermarks on the screen, but they do sell maps in all sorts of sizes that they will send straight to your home if you need a hard copy for your trip.
Mapquest – Better suited just for driving directions but if you can’t seem to find any good aerial photos on the other sites, try Mapquest just in c