Bangsapan is a small beach town around an hour north of Chumphon city in Prachuab Khiri Khan province. It offers a couple of interesting islands off the coast where some good diving can be had. The biggest and most popular island is Koh Talu but there are several other small ones around it. A short drive north is another sleepy beach town called Ban Krut, a fishing village with a 30km long beach and a few resorts. These two locations are quite far from the tourist trail but can be popular with locals, they make an excellent getaway destination with some diving thrown in for good measure.
More info about Bangsapan can be found here: Bang Saphan Guide