Hi carrigale,
It sounds like Mahoe Bay on Virgin Gorda fits all your requirements, although ultimately it depends upon your budget. Here's the link to the villa we stayed at. If you would like to see our trip pictures let me know. Good luck!

http://www.caribbeanway.com/villa-page/ind/106143.asp

What about Anguilla? Cap Juluca or CuisinArt or Cove Castle. Very safe, clean, fab food abounds, friendly people, GREAT beaches. You can find a link to their tourist board here
http://www.destinationcaribbean.net/index.php?option=com_weblinks&Itemid=183

I would suggest Montserrat but all of the beaches there (except for 1) are black. You will, however, have the luxury of having the beach to yourself. Check out wwwbunkumbeachguesthouse.com, + I can send you a few pics if you have an interest.

What about Parrot Cay, Turks & Caicos?

For what you have just described, peace & quiet and relaxed atmosphere can best be found in either Anguilla or Provo T&C, both offer gorgeous white sand beaches and clear turquoise waters, quite possibly the finest anywhere in caribbean.
for a private villa with plunge pool , Cap Juluca in Anguilla is 5 star all the way. for a nice resort in safe surroundings try Somerset, the Palms point grace or grace bay club in Provo.

Definitely Anguilla-friendly people, beaches incomparable, beautiful clear water, fantastic dining, quiet. Cap is my favorite resort, but the pool isn't great. Lots of villas available for rent with a pool, other hotels like Malliouhana and CuisinArt have pools too

Take a look on my website and you find 1000 reason to go to St. Barth.
www.iledestbarth.com

Ingo

While St. Bart(h) is very chic and upscale, it's not exactly quiet and doesn't have the calmest clearest water of the recommendations you have recieved. For as small as St. Barth is, it gets quite a few tourists, and is fairly active.

You really have described Anguilla and Turks and Caicos.

Anywhere in Anguilla you'll get what your looking for-and as a bonus you'll get the best restaurants in the Caribbean. Any resort in Anguilla describes what you are looking for, and of course any villa. Not as many villas to choose from on the beach, as Anguilla restricts individual construction on the beach.

T&C, check out Turks and Caicos Club-small boutique hotel (only 22 rooms) that are are complete with full kitchens, living rooms, and huge balconies. It's on a gorgeous strecth of beach, a block away from excellent off the beach snorkeling, and includes a full American breakfast. Now through middle of December, they are offering excellent specials (free nights, others) You get the feeling is pretty much to yourself, like a mansion, yet some amenities and pampering of a resort.

For more upscale, check out Parrot Cay (one of my favorites), Amanyara, or Point Grace.

T&C also has numerous villas all over the island, start with www.vrbo.com or check out rentals listed at www.tciway.com-click on where to stay.

Happy birthday!

Another vote for T&C or Anguilla. You won't be disappointed in either.

I'm on a similar search, and we have been to St. Barts and Virgin Gorda which were two suggestions made here and St. John which was not. We liked St. Barts the best of the three, Virgin Gorda next and then St. John. Virgin Gorda has fewer tourists than St. Barts but it really depends on what time of year you go. Anytime after April, things are pretty slow on most of the islands. St. Jean Beach on St. Barts was calm, blue and beautiful. Flamands is lovely too. There are tons of villas available in all price ranges. I don't know your price range, but we liked the villa Santal. On Virgin Gorda, we rented Open Deck on Mahoe Bay. We go in May to pay the off season prices. If you want to know more you can see pics and trip reports on www.maggiwun.blogspot.com