Here's some ideas:

Yosemite National Park (don't miss it!!!)
Sacramento--California State Railroad Museum, Sutter Fort State Historic Park
Sutters Creek--Sutter Gold Mine (and other small Gold Country towns)
Lake Tahoe and Truckee
San Francisco--Alcatraz, Golden Gate Bridge, Chinatown, Lombard Street, Cable Car Museum, Cartoon Museum, Fort Point, View from Twin Peaks (on a non-foggy day), Golden Gate Park, Fisherman's Wharf/Pier 39, Teatro Zinzanni, Beach Blanket Babylon
Marin and Sonoma Counties--Marin Headlands and Point Reyes National Seashore, Muir Woods (redwoods), Wine Country, Jack London State Historic Park
Monterey area--Monterey Aquarium, Carmel,John Steinbeck Museum (in Salinas)