The top-spot for seafood is the Bien Vinh Hao restaurant -- the seating doesn't take full advantage of the seaside location, but some of the tables have good views. The menu is standard for a Vietnamese seafood places -- fish, crab, shrimp, eel, with a variety of hot pots and non-seafood dishes available. This is the one place on the beach locals will travel to just for the food. Dishes start in the 20,000 VND range up to 60,000, and higher for market prices some fish.
The Pandaran Guest House has a perfect little cafe/restaurant on the water, taking full advantage of the location by providing ample seating in little nooks and crannies along the rocky coast. It's a great place to sit and watch the boats bobbing in the sea, listen to the waves plashing against the shore, and feel the cool wind blowing off the water. Consumption here is best limited to refreshments, with the food menu not extended much beyond noodle dishes.
The Vietnam Scuba Resort offers some of the only Korean food in the entire region -- very authentic, home-style fare prepared by the Korean chef (A.K.A., the owner's Mom). There aren't that many Korean dishes listed on the standard menu, but everything is served Korean style, with ample side dishes and rice. If you know your Korean food, ask for what you want -- we had the twaeji kim chi tchigae (kim chi stew with pork) and ordered it maewayo, (spicy).