Last fall I stopped in for a haircut at the salon in the SFO international terminal. The owner mentioned to me that she offers shower facilities; I don't remember the fee. Seemed like a good deal though.

The salon is located in the public area of the international terminal, north side main floor. It's kind of hidden on a balcony overlooking the escalators. I was in the terminal last month and she was still in business.

By the way, on the south side of the international terminal in the public area is a small SFO museum that traces the history of the airport. Next door to the museum is an airplane model store.