Dungeon Map Doodler - Dungeon Map Doodler is a free to use drawing tool accessible from any web browser. Easily create maps for your favourite tabletop RPGs in minutes!
PyMapper - Drag and drop tile based mapping program.
Dungeon Scrawl - A dungeon scrawling tool by ProbableTrain
Fractal Mapper - With Fractal Mapper, creating worlds has never been so easy!
Tiamat - Tiamat is Web 2.0 Tile Mapper; Ideal for creating miniature scale maps for role playing and miniature games.
Inkarnate - A free-form map editor for role-playing games, focusing on overland and continental maps.