If you're in Napa or Sonoma contact these guys.
We took 2 tours with Platypus. One in Napa and one in Sonoma. Both were really good, concentrating mainly on small family-run wineries. Both guides (Casey and Steve) were very knowledgeable and kept the whole group entertained throughout the day. It's a great way to visit 3 wineries and relax knowing they will drop you outside your hotel on the way home.