Tiled
Flexible level editor
...Tiled is a general purpose tile map editor for all tile-based games, such as RPGs, platformers or Breakout clones. Tiled was originally written in Java. In 2008, work began to develop a faster, better looking, and easier-to-use version of Tiled based on the Qt framework. This decision was made as the Qt framework has a greater feature set than is offered by the standard Java libraries.