Depends what you're into. There's a little of everything in the Bay Area.
San Francisco is about half hour away. Lot's of sightseeing stuff - Golden Gate Bridge, Alcatraz, Fisherman's Wharf, etc.
Past the Golden Gate bride and a little further north, you have Muir Woods with the giant redwoods.
If you're into wine (or spas for your wife), Napa, Sonoma, and Calistoga are 1.5 hours away.
Heading south, Carmel and Montery is about 2.5 hours away - Pebble Beach golf course, the scenic 17 mile drive, Montery Bay Aquarium, and Steinbecks Cannery Row.
-Dan