If you want to tour one of the big companies, find a friend/acquaintance/recruiter, and catch lunch. These companies compete on quality of meals...
Also, if you're going to rent a car, I highly recommend visiting some Redwoods. The best around are in Big Basin about an hour south of SV. There are also some just north of SF in Muir Woods.
Unfortunately I have no contacts in these big companies.
That's a good shout on the redwoods, I had no idea this was on offer near the SF area, thanks.
Also if you end up renting a car you may want to check out Yosemite (3-4 hr drive). That is on our list.