Take the silverado trail into wine country if you're going all the way to Napa. It's the road less traveled and there are some really excellent wineries to be tasted.
In sonoma I would highly recommend Gundlach Bundschu
http://www.gunbun.com/ , great cabernets. It's not far off Sonoma square and there is Ravenswood Winery nearby known for it's Zinfandels.
Stinson Beach, Point Reyes National Seashore, Muir Woods, Mt Tamalpais State Park, Samuel P Taylor State Park all excellent Marin attractions.
Have fun!
