On the back (west) side of the island is Koh Rong's finest beach, a 7km stretch of drop-dead gorgeous white sand, dubbed Long Beach (also called Sok San Beach after the fishing village at its northern end). Longtail boats head here from Koh Tuch pier, depositing sun-seekers on the sand for a day of sunbathing and swimming. There are simple resorts at the north and south end of this beach, with virtually nothing in between.
During our last visit, one of the basic resorts on the southern end was being knocked down to make way for a new hotel construction, so expect part of this sandy sweep to see more development in the future.