I vote for Gloria Ferrar Champagne caves.
They are located at the very southern end of Sonoma, near the Bay.
I like them because it feels more like you are having a drink instead of rushing through some tasting.
You pay for a full glass of champagne (they also have some regular wines). You get a little dish of spiced almonds. You can either sit inside, with the fireplace or out on the terrace (my favourite), where you look across about half a mile of vines towards the road. It just feels really relaxing to me..you sit down, you have a nice drink, you have a nice view...they also offer tours of their champagne operation, which I found interesting...now I know what the original riddler does.

Basically the entire strech of counties north of the bay are the north bay wine country. It ranges from Russian River in the west towards the silverado trail in the east.

Like I said, I went last Sat after thanksgiving and it was pretty empty, and the vines were really gorgeous.

Have fun!