Source mapper
This tool visualizes a source map, allowing you to debug your source map generator.
It's a bit crude, but gets the job done. Hope it helps you.
There are some examples you can load, or you can drop the index.html into an existing project and paste the source map of that project. It should then load your map and files and allow you to test your own maps.
Live demo at http://sourcemapper.qfox.nl