darkFunction Editor is a 2D sprite studio that allows you to rapidly define spritesheets and build complex animations, which can be exported as animated GIF's or as XML to be loaded into your game engine. No more messing around in paint programs or manually tweaking coordinates!
Latest build: http://darkfunction.com/files/dFEditor%20Installer.jar
For feature list and screenshots see here: http://darkfunction.com/editor/
For example output and third-party plugins see here: http://darkfunction.com/editor/documentation