This seems like a good place to drop this..
http://www.scriblink.com/
Team Captains might want to play with it. Let me know your impressions please.
Its a WhiteBoard. So far its the simplest I have found which allows (A) uploading an image and (B) saving the board to an URL you can give out. This should allow a team to upload the map image and scribble on it.
Its one of my jobs to have an idea of whats available and for wht purposes. And altho I dont work for Shrapnel anymore I will probably make a recommendation to them to upgrade the CHAT we have on this forum to some sort of a WhiteBoard. Possibly with VoIP abilities also (voice chat). It just seems a good idea for a strategy wargames company that has team games.