CL is pretty definitive, although walking around and looking for signs or working your network can yield results. If you have a smart HR department they're often helpful as well.
Especially in San Francisco it's going to be brutal and pretty much a full-time job. Keep a rental resume (metrorent app, credit report, letter of reference, etc) handy and try offering to pay the move-in cost on the spot if you fall in love with a place.
It's significantly easier to find a place if you're (a) willing to share an apt (there are tons of professional people around splitting fairly nice apartments) or (b) willing to live in a professionally-managed apartment complex/tower/whatever. If you go with an apt complex in SF, avoid Skyline/CitiApartments.