North Napa:
Sterling - wines are ehh, but the whole trolley ride and drinking on the top of a mountain is quite cool, worth it if you have extra time
Twomey - if you even think about drinking Merlot, that is all they make here - fantastic.
Frank Family - Awesome, awesome wines - great under the radar wines
Joseph Phelps - nothing special in terms of the winery, but their wines are really good (a little over priced for me, but really good).
Cakebread - a staple, you taste in their backroom, you normally have to wait to go with a group. Wines are good - mostly priced by reputation, but they are still good and for $10 bucks for a glass and good wines? Worth it.
Nickel & Nickel - yes, please.
South Napa:
Silver Oak - more central, but, only have 1 wine, and it is $10 for a glass and 1 glass of wine - I think it is fantastic and well worth it, others on the board have disagreed. You won't spend a ton of time here.
Domaine Carneros - my favorite Cali sparkler - beautiful chateau, very upscale, great sparkling wine (and their pinot isn't half bad either).
Acacia - call ahead to book a time, great carneros pinots
Darioush - really cool turkish style winery, wines are good, and tough to find
My (way too long) 2 cents.