PyMapper - Drag and drop tile based mapping program.
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.
Tiled Map Editor - Tiled is a general purpose tile map editor.
Inkarnate - A free-form map editor for role-playing games, focusing on overland and continental maps.
DUNGEONFOG - Online authoring tool to draw rpg maps & dungeons, create dynamic notes and share your maps online. Create dungeons, world maps and more with the easy to use map editor and create your game master notes dynamically.