One that comes to mind is Cartogropher. Can be found
HERE
Cartogropher is the main part of the mod. There are plugins that can show various things.
In your case you have
Cartogropher_Quests ... Shows Quest Givers
Cartogropher_Trainer ... Shows Trainers
Cartogropher_Vendor ... Shows Vendors.
Only problem with these type of mods is that they all require you to get this info yourself by finding it. It will automatically place an Icon on your map for you for anything new it finds as you locate and interact with it.