Google Maps
Google Earth; Earth View in Google Maps
Open Street Map http://wiki.openstreetmap.org/wiki/Main_Page
Map My Ride http://www.mapmyride.com
Ride with GPS http://ridewithgps.com
Strava Cycling: http://www.strava.com
Strava Multiple Ride Mapping Tool
http://geocommons.com/
http://bicycling.about.com/od/howtoride/tp/mapping_tools.htm
http://nationalmap.gov/
http://www.randmcnally.com/
http://www.caliper.com/
http://en.mappy.com/
http://www.mapchannels.com/
http://www.zeemaps.com/
http://www.esri.com/
http://articles.businessinsider.com/2011-01-05/tech/30039704_1_mapping-technology-housingmaps-zip-code
http://open.mapquest.co.uk/
Microsoft's Terraserver
NR Canada's digital map server
US Census Tiger Mapping Service
The OnEarth server for MODIS is currently being phased out and replaced by the Global Imagery Browse Services (GIBS) provided by the Earth Science Data and Information System (ESDIS) Project: http://earthdata.nasa.gov/gibs
http://topofusion.com/