The world image layer comes from ESRI with a min resolution not as good as Google Satellite, but
it's available as REST service and in arbitrary projections (tested with EPSG:900913, 4326 and 31466) and available at no cost, regardless of use.
zoom to Berlin London Paris New York World WFS location - read more...
The WMS layer from MetaCarta is styled by SLD_BODY to show only the borders of the countries above the world image layer. To change the style by SLD and an extern SLD-file seems not to work.