San Fran is great, especially if you love food. If I were you, what I'd do is:
1. Fly in to SF, spend a day or two wandering around/eating/taking in the sights.
2. Rent a car, drive up the coast to Seattle.
3. Check out Seattle for a day or two. Also awesome food, nice scenery around the city, etc.
4. Cross the border and visit Vancouver—awesome city.
5. Drive back, hit Portland, Oregon, on the way.
6. Drive from Portland to Yosemite National Park in northern California.
7. Drive from Yosemite back to San Fran.
8. Fly out.
Car rentals aren't cheap, but they're pretty affordable ($200ish a week for a little econobox if you shop online).
An Australian guy on another board I post on just planned a similar trip, except he's going from LA to the east coast on a two-month-long road trip. You can check out his planning thread
here.
I believe Scott Andrews (DuCK) just did a long trip to the US, including San Fran, a couple months ago. He might be able to give you some advice, too.
Good luck! Should be fun.