I went to Tru spa once. It was nice. It is located in SF.
Day Spa San Francisco - Tru: Facials Massages Pedicures Manicures

Some of the nicer hotels also have really nice day spas.

I am not sure if it is in yet but Blackhawk is suppose to be getting a spa in the Blackhawk plaza.

Check Pleasanton too. I recall reading about one there that got a Best of Pleasanton award.