Eric,
Not sure how many nights you are staying up there, but I'd check out the concierge desk to see what they'd recommend. Last time we stayed up there at the Marriott in Napa, the concierge was able to recommend a lot of new places we've never been to before. They were also able to give us a bunch of complimentary passes and also some 2-for-1's which help.
We've been to tons, but these are ones I would recommend:
V. Sattui - popular, crowded, and no longer free, but it's great for beginners of wine. Nice picnic area and they have a deli for fresh food, or a BBQ outside.
Arger-Martucci - recently discovered this place on our last trip a few months ago. It's family owned and the manager gave us personal service. Not crowded and wine was enjoyable.
Peju - awesome wines. The pourers are really friendly.
Cakebread - awesome wines too. Tastings by tour only, so you'd have to make reservations ahead of time.
Silver Oak - hands down the best Cab you will find anywhere. Only been here for release days, but I think they have a tasting room in Oakville that's open to the public. Definitely would go here if you have the time.
Frog's Leap - haven't been here, but I've heard great things about it.
And if you are your wife are into sparking wines/champagne:
Mumm - good sparkling wine, and usually have an awesome art gallery.
Domaine Carneros - awesome mansion to sit in front of. Good wines too.
And I'd recommend mapping out where you want to go ahead of time, or you'll be driving up and down the Silverado Trail.
