The Most Beautiful Thai Destination

OK guys, some help please. If I have say 5 or 6 nights to spare and want to travel from and back to BKK, short flights OK, where would you recommend as the most beautiful Thai destinations? Not so interested in Gay facilities, just the best of Thailand, with beautiful beaches/Islands and some nice things to do/see?

I have been to Krabi/Pi Pi, Phuket and Pattaya, but can't say they are heaven on earth unless I'm just staying in the wrong local locations!

Thanks![/u]