We had a great day at the Exploratorium - for free! Smithsonian Magazine's Museum Day made is possible, and they are doing it again on Saturday, September 25th. Download an admission card here, and get into museums like Hiller Aviation Museum, Coyote Point Museum, the Exploratorium, Cartoon Art Museum, Contemporary Jewish Museum, Bedford Gallery, Blackhawk Museum, Chabot Space & Science Center, and others.
The card is good for you and one guest - one card per household. Participating Bay Area museums are listed here.