My kids and I have participated in Summer Reading Programs since they could toddle into the library (actually, maybe even before that). They love filling out the little forms, and collecting their prizes. Every county library in the bay area has a Summer Reading Program for kids, most of them begin today, June 14th. Some local bookstores also have reading programs, and kids can earn free books.
For more information on the library programs, here are the county library websites:
Half Priced books, that has several locations around the Bay Area offers a Summer reading program as well. Kids can earn a $3.00 store credit each week for reading 15 minutes a day, 5 days a week. You can read more, and print out the reading log at the Half Priced Books website.
Boarders Books, requires kids to read 10 books over the course of the summer, and they can earn one free book from a preselected list. To see the reward book choices and print a log form, check out the Boarders website.
We are also fortunate in the Bay Area to still have some smaller, independent bookstores. I don't know if any offer summer reading programs, but many sell used or hard-to-find books, and are just great places. Here is an independent bookstore finder, so you can see what shops are in your area.