OpenStreetMap volunteers have just finished a Public Domain list of London Tube stations.
The list has been gathered by people using GPS units – so it is not a derivative of other OSM data. This means that it can be released under a Public Domain license, so you can do what you want with it.
I’ve knocked up a quick CSV of the data that you can grab from here
Update – To get hold of the data, visit the OSM wiki page.