Phu Quoc

Phu Quoc is the biggest island in Vietnam with 574 sqkm. It's located 40km off the south-western most tip of Vietnam and just 11km off the Cambodian coast.

Phu Quoc is Vietnam's most popular, if not only, holiday island. It has about the same size as Phuket (in Thailand) but draws much less number of tourist.

Wikitravel says:

Phu Quoc is ringed with some of most beautiful beaches and best seafood in Vietnam. Phu Quoc Island served as a based for French missionary Pigneau de Behaine from the 1760-80s and at one time he provided shelter here for Prince Nguyen Anh (later Emperor Gia Long) when he was being hunted by the Tay Son rebels. During the Vietnam war there was little fighting here but the Island was used by the Americans as a prison for captured Viet Cong. Phu Quoc is not really a part of the Mekong delta and also doesn’t share the deltas extraordinary ability to produce rice & fruit due to its soil quality and inaccessible terrain. It is however home to the best Fish sauce (nuoc mam) in the world also reputedly known to produce high quality pepper and fantastic seafood. Another point of interest in Phu Quoc is the island’s native dog; this dog was originally a wild animal and later trained as a hunting dog by local people. These days they are very domesticated and it’s unusual to go anywhere on the island without seeing one of these dogs! These animals have unusually sharp teeth (as they tear their food when they eat it rather than bite) and have claws that over the years have been conditioned for catching their prey and are razor sharp.

Wikipedia says:
Phú Quốc (known as Koh Tral by Cambodians) is the largest island of Vietnam. Situated in the Gulf of Thailand, the island is part of Kiên Giang province. The district of Phú Quốc includes the island proper and 21 smaller islets. The district seat, Dương Đông, which is located on the west coast, is also the largest town on this island, whose total area is 574 km². The island's monsoonal sub-equatorial climate is characterized by distinct rainy (June to November) and dry seasons (December to May). The annual rainfall is high averaging 2,879 mm. In the northern mountains up to 4,000 mm have been recorded. April and May are the hottest months with temperature reaching 35 °C. ... read more