A cross platform (python) implementation of John W. Ratcliffes' excellent texture-atlas algorithm written in C (http://code.google.com/p/texture-atlas/).  This project takes things further than texture-atlas by creating the atlases from the information generated by the texture-atlas algorithm.  It can handle any image type and can create power of two atlases of any image type also.  It also finally generates an xml atlas dictionary for loading and using the images at runtime in your application.  Please note, this script depends on the Python Imaging Library (PIL) which must be installed on your system before running (available from http://www.pythonware.com/products/pil/).