SpriteMapper is a Java program which creates sprite maps (or sprite sheets) from a set of input images.

Similar programs include Zwoptex and TexturePacker which unfortunately are not open sourced.

It supports rotation, trimming, Zwoptex 2 plist format (in time others too) and (again in time) many different layout algorithms and heuristics plus it contains an Ant task . Patches are welcome :-)

Documentation included in the archive but here is an example sprite map.