Dungeon Tile Mapper - Dungeon Tile Mapper is a web based tile mapping tool that includes many official D&D tile sets.
Tiled Map Editor - Tiled is a general purpose tile map editor.
Fractal Mapper - With Fractal Mapper, creating worlds has never been so easy!
Tilesetter - The tileset designing software.
Tiamat - Tiamat is Web 2.0 Tile Mapper; Ideal for creating miniature scale maps for role playing and miniature games.
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.