Today, Plum District is offering 1 adult &1child admission combo to the Exploratorium in San Francisco for $15 (it's normally $25 for the pair). To qualify, kids must be 4-12 (under 3 is free anyway), and you can buy 4 tickets a person. Valid for entrance Tuesday to Friday, starting when you buy it, but expiring 11/10/10 (next month). A few other restrictions (no Tactile Dome, not valid toward membership etc.)
For the next three days, Mamapedia is offering gorgeous ice cream cakes from Maggie Mudd in San Francisco. You buy a $25 voucher, good for $50 in ice cream cakes (if you don't use the entire amount on cake, you can use the rest for ice cream). They also have vegan options! And the price includes FREE delivery in San Francisco. You can buy up to three vouchers, and you have a year to use it.
I've not heard of Shoe Buy before, but Groupon San Jose is offering a $30 voucher for $15 today. It's an online store with free shipping and no tax in CA. If you don't use the entire amount in one purchase, the remained can be used later.