The best by far beach I have stayed on was Phi Phi Leh, amazing views across the Bay and the sand was like talcum powder.....Sadly not such a similar storynow, having just revisited the island after the Tsunami. Much of it's natuaral beuaty has been obliterated, althought the locals were still as amazingly hospitable and welcoming returning tourists.
2nd to that, I have had the pleasure at the Sandy Lane on Barbados west coast. The beach is pure white and so soft to walk on. Better still are the catamaran's waiting on the shore, ready to take off a cruising round the carribean, champagne included!