Silverado Winery - owned by Diane Disney Miller - also sits on a beautiful site and makes excellent wines. It's in a region (Stag's Leap district) with other excellent reds - not on the main Hwy 29 but on the Silverado trail just east of it. Clos Du Val is there, Stelzner, Stag's Leap ( of course), Pine Ridge. Usually not as heavy traffic as 29. Some wineries require reservations now btw - you should check the napa valley websites. On 29 is Coppola, where he has some set pieces from the Godfather.
Champagne tasting is fun and a bit different - Schramsburg does a great one ( res required). A lot of people enjoy the tram up to Sterling, but I've never done it because I didn't want to waste an hour in the line. Vi Sittui is fun -- they have a deli where you can buy stuff to eat in their picnic area. Chateau Montelena is excellent too - esp the reserve tasting.
My hubby and I always split tastings btw to save money and our palletes -- some places charge as much as $20 for reserve tastings which are usually a LOT better.
And I'd be remiss if I didn't mention Solovino, which is owned by my daughter-in-law's folks!
I LOVE Napa! Lots of fun.