Everyone will have different favorites.
A few I recommend to people:
- Nickel & Nickel: great estate cab's and all red tastings
- Joseph Phelps: beautiful winery setting and a wine I enjoy to drink at home
- Artesa: Not actually in Napa but in Carneros. If you're a fan of Pinot Noir, Carneros is a great region for Pinot grapes. Artesa has a neat view looking south towards San Fransisco Bay and a lot of modern art.
As evidence by everyone will have their favorites... I disagree with the poster above on the quality of Silver Oak wine (I think its great) but their tasting wasn't my favorite.
To each his own. That's why their are so many. My other advice is pick some small obscure wineries and pop in for a visit. They usually don't require reservations, have generous tastings and are happy to sit and chat with you.
[This message has been edited by Ags03 (edited 7/10/2012 10:31a).]