You may be surprised how many people do not advertise in the paper but do post notices in their windows. Being able to provide a credit report on request may give you an extra edge in the rental process. TRW consumer Assistance provides one free credit report per year. They may also assist you with any credit problems. Look in local papers such as The Independent, Bay Guardian, Mission News, Potrero View.
Most areas have a local paper.
If you look in the Chronicle or the examiner, it is best to get the Sunday edition and start looking early Sunday. Go prepared to fill out application forms and provide references. This list is by no means everything that is available in the city, but hopefully it's a good start for you.