Lyme Regis was lovely when we went, the seafront was very tastefully landscaped and there is the famous "cobb" - like a huge curved jetty out to sea, where the film The French Lieutenants woman was filmed.......... of course just remember you need good weather, as with anywhere, places look totally different in pouring rain!
Mudeford Quay and Christchurch near Bournemouth are quite nice too but personally I don't think you can beat Cornwall, especially the little coves on the Lizard Peninsula.