Going to be there for a week. I've got Castro and Fisherman's Wharf and Lombard Street and Chinatown and the Pacific Ocean checked off. Anything else y'all can think of? Oh, and North Beach!
Go up the twin peaks, you’ll have a stunning vista of the Bay Area. It drives home why people will say it’s one of the most stunning setting for an urban area. If you’re mobile, Mount Tamalpais is gorgeous too, and a cruise along Highway 1 is always a great time, plus there’s little parking turnouts going down to itty bitty beaches as well. In The City itself, my info is rather out of date (and we honestly didn’t go up there too often even when my brother lived there). Fisherman’s wharf is hella touristy, which probably surprises nobody but it’s still disappointing. I presume you’ll hit up City Lights bookstore while you’re in North Beach. Don’t forget Golden Gate Park and the DeYoung museum. Also the ruins of Sutro Baths are interesting. I don’t know the current status of the Cliff House (it’s long had $$ problems), but that’s another really historic SF institution. That’s all I’ve got at the moment.
Tony's Pizza Napoletana (Tony has beaten the Italians in Naples in Pizza contests) Mission Bowl (for the best burger in town) As jcp123 said, Fisheman's Wharf it just a tourist trap, so is Ghirardelli Square, but you have to get a sundae there after you have a meal at McCormic and Kuleto's Maybe the Painted Ladies across from Alamo Square Lombard Street is just another street with lots of traffic Alcatraz is interesting Hiking or biking around Angel Island If you have lots of time, go to Muir Woods and Stinson Beach Sausalito is a great little town to visit on the north side of the GG Bridge Maybe a Hornblower or Blue & Gold Fleet evening/dinner cruise Napa and Sonoma wine tasting is always good to do A good way to see a number of sites in a short period of time is the Big Red Bus Hop on, Hop off trip
Lots of great tips here. The Golden Gate Bridge is a great walk or ride. If you take the first right after the bridge ends, there's parking lots and you can get some great views there. Food! Some of the best restaurants in the world are in SF. French bakery for breakfast, clam chowder in a bread bowl for lunch, Asian for dinner is what I would do in just one day. The marina area is an excellent place to visit or just hang. Close to the bridge. Last but NOT LEAST, the Haight/Ashbury area, just outside Golden Gate Park, once the start of the Hippie era. Hippie Hill is just a short walk into the park. Good place to get high and soak in the vibe! Stay away from Union Square. That's a problem area these days tho it used to be a big tourist area because the big stores and hotels were there, now many have closed. You might encounter homeless people and Lord knows what around there and elsewhere.