Two wineries- seeing as you are starting in Napa at the Fatted Calf, proceed over to Silverado Trail and hit Joseph Phelps first. Great views and great wines. Ask them if you can enjoy your lunch out on their patio and if it is a weekday you are probably in luck.
Then on to Chappellet for a wine tasting and tour of the vineyards. Great wines and again great views.
Both of these wineries require a reservation so plan ahead.