I would definitely recommend Ogmore by Sea, otherwise known as Southerndown, I've done some drawings I absolutely love there. I'm going to Pembrokeshire tomorrow, I've heard Skomer Island is a sight to behold so taking my paints. I would also say Penarth near Cardiff for the cliffs, pebbly beaches and pier (really pretty pier). St Fagans is also excellent, I prefer painting the gardens as they seem to be permanently in bloom.