Canterbury which is a fantastic town, just a few (maybe one or two) stops on the train toward London. Both are highly recommended, but I haven't done Bath or Cambridge.

About the Cliffs of Dover.. I did a walk along the shoreline that was so pretty and incredible. Just when you think you've seen the last cliff, another one comes over the visible horizon. Saw a fox, there, too. Really stinking cool. Dover castle is really cool, too. Enjoy