Your best bet might be to go to Good Old Gold''s website. They have great pics up, and on the first screen you can see an example of each type of shape. You can click on the shape to see more examples.
The princess is very square, with sharp corners and the look of almost an X across the stone.
A radiant is a cut corner stone with more steps up to the table, less of an organized look to the interior when compared to the princess.