Here are some of my favorites, add yours in the comments!
2. http://www.google.com/mapmaker (Because everything Google does is awesome)
5. http://www.scribblemaps.com/ (There's an app for that)
6. National Geographic! http://education.nationalgeographic.com/education/mapping/interactive-map/?ar_a=1
7. http://batchgeo.com/ One of my favorites, if we already have the data.