http://www.zeesource.net/maps/home.do

different? www.zeemaps.com

http://www.communitywalk.com/
CommunityWalk.com has been the absolute best. They have customizable URLs and map markers and you can bulk upload data and then edit each data point by clicking. You can also export data. Also, they emailed me right back when I had questions. They are also free if you will tolerate ads on your map, and very affordable if you want to be ad-free--they use a subscription model, starting at $5/month for 1 map. I am a convert.

http://socialsoftware.weblogsinc.com/2006/03/18/community-walk-redesign-makes-google-map-more-attractive-and-fun/

http://whoissick.org/sickness/

www.mapbuilder.net

http://www.dataplace.org potential for clients to make data

http://nationalatlas.gov/natlas/Natlasstart.asp - forAg, Bio, Climate, Environment, history, people, water

www.dabbledb.com
www.wayfaring.com
www.mappoint.com
www.frappr.com
Microsoft MapPoint