According to Forbes, the top spas are:
The Spa at Chiva Som, Hua Hin, Thailand
The Spa at CordeValle, San Martin, Calif.
The Spa at The Four Seasons Resort Bali, Jimbaran Bay, Bali, Indonesia
The G Spa at Hotel Gansevoort, New York City
The Greenbrier Clinic at the Greenbrier, White Sulphur Springs, W.V.
SpaHalekulani at Halekulani, Oahu, Hawaii
The Spa at The Lanesborough, London
The Spa at The Ritz-Carlton, Key Biscayne, Fla.
Chi Spa at The Shangri-La, Pudong, Shanghai, China
The Spa at Stoweflake, Stowe, Vt.
The only one I've been to is Stoweflake's, which is gorgeous.