Trefethen for Riesling. Markham for Moscato. Frog's Leap for Zinfandel.
Robert Biale is great for Zinfandel.
The Napa Vintner's Winery Finder site is very helpful in searching for wineries by varietal:
Note: Just because a winery produces a certain varietal does not necessarily mean that it is part of their current tasting flight (particularly true of dessert wines like Moscato). I suggest calling to ask what wines are in their current flight.
I find it worth mentioning that the wineries in Lake County (~90 min drive from Napa Valley) have gotten a lot of acclaim in recent years for their Rieslings. Not sure if that might be compelling enough for you to possibly make a day-trip up there.
Napa Valley Bike Tours & RentalsEdited: 10 June 2018, 06:12