I always enjoy tasting at Duckhorn (as I always enjoy the taste of Duckhorn!). The winery is just east of Route 29 and tastings are held in the estate house on property. In warm weather, feel free to sit on the porch and enjoy your SB or Napa Cab (and the Howell Mountain Merlot is hard to beat).
Tastings are $10 for 3 current releases or $20 for the 3 current and 2 limited release wines. The winery is open every day (save a few national holidays such as Christmas & New Year's Day) for tastings. Estate tastings and tours may be arranged in advance ($30 for estate tastings).
I highly recommend cellaring some Duckhorn for future consumption (and don't forget sister wineries Paraduxx and Goldeneye).