My mom visits in October and I really want to go to the California Academy Of Science when she does. It's new and supposed to be really nice. I actually first heard of it when I saw the construction of it featured on one of those shows on TLC or Discovery. Extreme Engineering or something like that.
http://www.calacademy.org/
Also, go eat here
http://www.scomas.com/
Obviously, if it were fall or winter I would say head down to San Jose to catch the Sharks but oh well.
Also, if you want a little drive, Monterey/ Carmel is nice. You can visit Pebble Beach if you like golf and you are into $150 lunches! 17 Mile Drive is also something else if you want to see where some real old money hangs out. Anyway, a couple of my favorite places and one that I want to visit