Eh... if you go through SF, you could skip 21A, but Speakeasy and Cellarmaker are both good stops. Speakeasy in particular is fun, if you've got some time – they're out of the way, but they've always got a couple things on that you can't find in the store, and the taproom has this fun prohibition-era speakeasy vibe.
If you go the East Bay route, Drake's is definitely worth a stop, they've always got a couple crazy barrel-aged creations on tap. Jupiter and Triple Rock are sister brewpubs in downtown Berkeley which might be good stops around lunch time, Jupiter does a tasty pizza, Triple Rock solid burgers/sandwiches, and both an eminently drinkable lineup of house brews.
If the heat is getting to you as you drive down the Peninsula, you can stop at Gourmet Haus Staudt in Redwood City – they don't brew, but they've got half a dozen nice, refreshing German imports on tap, and a shaded biergarten to sit and enjoy them in.
San Jose has a bit of a budding local craft brew scene going on, but, alas, I can't tell you too much about it; it's too far of a schlepp on public transit, and beer tasting isn't much fun when somebody's gotta DD.