BayAreaFreeFi.com is now serving up verified and confirmed free wi-fi hotspots for the San Francisco Bay Area. From as far south as Carmel and Monterey, through Santa Cruz, San Jose (and the South Bay), Palo Alto (and the rest of the Silicon Valley), all the way through to San Francisco, Oakland (and others in the East Bay).
This site also has a WAP version for your mobile phone for locating a hotspot from the road.
150+ verified and confirmed locations and counting.
Know of one you don't see on the listing? Submit new locations for approval.
(the database has been updated for nearly a year now, but is just being published)