Sounds like you know about this trip enough in advance to get on the Anchor Steam brewery tour wait list. It's a free tour, but you usually have to book at least six weeks in advance! (Which is why I haven't done the thing yet, but I've heard the stories of how great of a tour it is!)
As for other breweries, this is a pretty beer-obsessed area. You're just missing beer week by a few days! Anyway, Lagunitas, Russian River, and Bear Republic are all in the North Bay and are probably painfully obvious suggestions. Definitely also check out Drake's in San Leandro while you're over here, and I'm personally fond of Devil's Canyon in San Carlos (tasting room only open on weekends) and Cellarmaker in San Francisco. 21st Amendment is also worth a trip, though don't go on a night when there's local sports happening if you want to stand a chance of getting a seat.
I don't know about homebrew shops in Marin, but Oak Barrel in Berkeley and Brewcraft in San Francisco are both great, in my admittedly newbie-ish experience.