If you're an Apple fan, don't forget to swing by the Apple campus store at 1 Infinite Loop. They had plenty of trinkets in there I hadn't seen at other stores.
Palo Alto is a pretty nice town in its own right although it's not culture central like SF. Must admit I'm not a big SF fan though and prefer heading to where interesting things are occurring rather than wandering about as a tourist.
If you have a car, Buck's of Woodside is worth a visit if you appreciate its history and significance in geek culture, but if you don't, there's little to actively see.