But seriously,
Redwoods are a must see, one of the most awesome living things on the planet.
Monterey Aquarium is very nice, Monterey is nice but pricey.
What sort of stuff are you looking for, nature, city, ocean, or a combo thereof?
Oh and DON'T FLY INTO SAN FRANSISCO!!!!!
To fly into central California use Oakland or Sacramento airport.
I'm serious here, S.F. airport is notorious.