To Ned Flanders
The island used in teh movie 'The Beach' is Ko Phi Phi in Thailand, a boat trip from the more well known island resort of Koh Samui
I went to Phi Phi some 12 years ago and it was awesomely beautiful. However, I do not intend going back as there has been a lot of development there, hotels being built and the film crew dug up the beach and repleanted it because paradise wasn't beautiful enough for them.
There was also CGI trickery used to make the lagoon ompletely closed. In real life there is a narrow gap out to the sea.
But Phi Phi is offered as a day trip from Samui and, because of the despoiling development, now you can book to stay there.