I call Sonoma the Tuscany of California.  Relative to its ritzy neighbor, Napa, Sonoma is decidedly bucolic.  And grittier.  I always say that Napa is where you will find wealthy people's version of a winery.  Sonoma, on the other hand, is the land of farmers.  Not just vineyards, but also olives, citrus, organic produce, and also cows and goats.  

The California Cheese Trail is found in Sonoma.  And so are empty beaches, happy people, proud artisanal farmers, and on a really good day, fogless, endless blue skies.

When to go:  I love coming to Sonoma during the last fringes of winter - February or March. This is a dead time for the hotel industry in general so you can really score some good deals on hotel rooms.  This is also the time of the whale migration northward from Mexico and if you've never seen whales spout in the wild, it is magic. And if that's not enough, mustard flowers are in bloom carpeting fields with bright yellow.