We really enjoy Mustards Grill too. I have a fond spot in my heart for it as a result of it being my celebratory restaurant of choice after completing the Napa marathon.
We came t h i s close to making a reservation at The French Laundry this summer, but two sets of friends that attended said that while, yes, it was excellent, they didn't think it was worthy of the price paid (around $1,000 per couple, including wine). So, we've landed on Greystone Restaurant instead, at the Culinary Institute of America mentioned above.
In Napa we really like Trefethen, and also Folie a Deux, but if you would consider popping over the hill, we're most nuts about Sonoma. Whereas tastings can be $20 on up in Napa, they are often free, or perhaps $5 in Sonoma, often waived with wine purchase. There are no shortage of good eats in Sonoma as well, with The Girl and The Fig being top on our list to enjoy during our visit this summer as well.