I would also say Stewarts Bay in Tasmania. It has the best sand and crystal blue / green waters. Tasmania is the place to come for beaches - pity the weather isn't warmer here tho. After travelling so much i have always said that Stewarts Bay is still the best beach by far.
In Hawaii i did enjoy Waikiki Beach because it was safe for everyone with Shark protection netting in the sea. You can also have turtles swim up to you, the water is warm, the sand is soft (and from Australia - Imported!)
There are lots of people on the beach - right out the front of our hotel which was up the end of the beach there was heaps a space to chill out and relax without the hassle of to many tourists.
In Zanzibar in Africa the beaches there are amazing, the water is so clear but there are allot of jellyfish so something to keep in mind.
Just some ideas for you. over 10 years ago