Some that I would recommend are:
1. Chateau Montelena - as you can see I am not the first one to suggest this winery in this thread.
2. Domaine Carneros - while their specialty is sparkling wines(and they make superb ones by the way), they give a great tour. I know you did not mention this type of wine, but this is definitely worth a visit and tour.
3. Ladera - Anne and Pat Stottesbury give a warm and unique tour and have some excellent wines.
4. Philip Togni - if you like old world styled wines, this is the place. The tour takes a little while but it is different and educational.
5. Reverie on Diamond Mountain. - Real neat tour, and sometimes a bit comedic as well, you can't go wrong here and the wines are excellent and underrated as well.
If you go to Kapcsandy, let me know how it goes, I am very interested in going there this year, I am on their mailing list.