Mae Ram Pheung beach, about 12 km south of Rayong City, should be one of the prime beaches in Thailand. It has beautiful sand, a backdrop of tall casuarina pines and palm trees, and a wide selection of sites with deckchairs and shade umbrellas.
There are also many restaurants (some little more than shacks) serving deliciously fresh seafood, which you can eat and enjoy with a cool drink in your deckchair.