I known that it is not exactly "standalone" UV mapping tool, but Blender has strong UV Unwrapping.
http://www.blender.org/features-gallery/features/#c3662
http://download.blender.org/demo/movies ... der242.mov
There is also reasonable priced tool Ultimate Unwrap 3D - I have not tested yet but it looks fine.
http://www.unwrap3d.com/

- By Mark Bell