Dolores Park in SF, Union Square
Walnut Creek, Stern Grove
Check out of host of local museums
Oakland Museum of California is free on second Sundays
SF Museum Of Modern Art is free the first Tuesday of each month and children 12 and under are always free.
The African-American Museum and Library in Oakland is always free
Asian Art Museum in San Francisco is free 1st Tuesday of the month.
For kids check out the Bay Area Discovery Museum in Sausalito the 2nd Saturday of each month, free for families 1 - 5 pm.
California Academy of Sciences in San Francisco is free 1st Wednesday of the month.
The Cartoon Art Museum in San Francisco, the first Tuesday of every calendar month is "Pay What You Wish Day
De Young Museum in San Francisco is free the first Tuesday of each month
Habitot in Berkeley their Free admission days are listed here
SF Zoo is free the first Wednesday of every month
Thursday Night Live in Old Oakland is the 1st & 3rd Thursdays 5:30pm to 9:00pm, June thru October on Washington between 8th & 9th, 9th between Broadway and Washington
Lakefest: Art, Wine & Food Festival on Lakeshore Avenue, August 1 & 2 10:00 am to 6:00 pm
Montclair Jazz & Wine Festival Sunday, Sept. 13, 2008 - 11:00am to 6:00pm in Montclair Village. Once again, Montclair will be turned into a pedestrian zone from 11:00 a.m. to 6:00 p.m. to host one of the fastest growing cultural events in the East Bay.
Out & About in Rockridge September 27th 11:00 AM to 6:00 on College Avenue between Claremont & Manila Ave (.6 miles) Free and hosting hundreds of artisans.
Horse races at Golden Gate Fields kids are free adults as cheap as $4.
If that doesn't keep you busy, well, I guess you'll have to make your own fun. Enjoy your summer!