My wife and I love visiting Sonoma and the many wineries. We have personal favorites, but there are so many we still haven't seen, and new ones opening every year. A few thoughts:
Wine tasting can be expensive so by all means utilize the Worldmark free tastings, and obtaining a passport can be beneficial as well. Note that if you have a Visa Signature card, there is a program allowing you to get free tastings at as many as 50 participating wineries. Some of the tastings may be somewhat limited compared to a fully paid tasting, but it's a decent way to see additional wineries without paying for tasting fees. Details can be seen at this website: http://sonomawine.com/visa-signature/
Also, the Wilson winery (who have excellent wines) is linked with a "family" of 10 wineries. If you become a member of any of the 10 wineries, you get tasting benefits at the other 9 wineries. Some are a distance from Windsor, but several of them are very close.
A fair drive south of Windsor is Cline. If we are in the area we make a point to visit as they have a broad selection of wines with a spectrum of price points. They have a great location with a history that links to the Spanish missions, offer onsite tours, and have ponds, animals and picnic areas that can offer a fun time. Also roughly in that area is Kunde, which has an interesting history as well.