A disclaimer on my recommendations...my DH and I are
not wine people, in fact it's rare that I like a wine (we live about 12 miles from Napa...and I know some people would think it a crime that we don't drink wine!

). Also, family and friends who have visited us aren't really into drinking wine either, so the places we go are mainly about learning how they grow/create the wine and good wine country scenic touring, not really about the wines we were tasting.
The winery that we take family to when they visit us for a good tour is the Benziger Family Winery (
www.benziger.com). They have a nice, small winery in Sonoma that has an excellent tour. You ride a tram out into the vineyards, get to tour inside their caves, and the times we've been there we received 4 wines to taste as part of the tour. For $10 each we think it's a pretty good deal!
The other winery I generally take visitors is Viansa, also in Sonoma (
www.viansa.com). We like this one because you can buy some nice picnicy type lunches there and they have a WONDERFUL outdoor eating area that you can look out over the valley as you eat your lunch. They also have quite a unique gift shop with lots of interesting items. You can sample wines there as well, but since that's not really what we're interested in we haven't done it so I'm not sure how much they charge.
I agree with the previous poster that Sonoma is a great little town to visit. The Visitors Bureau is right there on the "main square", definitely take the time to stop in. The ladies there can give you tons of brocheres, maps, provide recommendations (they directed us to Benziger originally), and also may have coupons for free tastings at various wineries if you're interested
Have a great trip!!