We purchased the Priority Pass for our first time visiting the wineries of Napa and Sonoma. There are many wine passes out there but this one is the best deal because it covers wineries in both areas (as well as many other wine regions.) Wine tasting fees, especially in Napa, can be exorbitant (the average fee is around $40 but some wineries charge upward of $100!) We visited 15 wineries in our week stay and saved almost $300 with the Priority Pass. Look around and you can also find discounts on purchasing the pass (we got a great deal with Groupon.)
If you are looking to visit the big name wineries, then this pass won't help you. However, it does include MANY wineries and chances are, any winery you hit in this area is going to have good wine. Do your research and you will find some off-the-beaten-track hidden gems (our favorites were Hans Fahden and Auburn James in Napa and St. Francis in Sonoma.) The pass also offers discount on other services (restaurants, wine train, bike rentals, etc.)
I would recommend this pass to anyone - especially first-time visitors - spending more than a couple of days in Napa and Sonoma.