In SF, almost every single apartment listing is captured through craigslist. This isn't the case in a lot of other cities, but here it is almost always true.

That said, there are a few websites that plot all craigslist postings onto a google map, which you can then filter by rent/bedrooms, etc... Padmapper is one example: http://www.padmapper.com/search/apar...San-Francisco/

Padmapper also has an iphone app - so my advice would be to find your neighborhood first, then circle out from there, looking for apartments nearby that fit your budget.

Go to a few open houses (they're listed on craigslist) just to get a sense of what you're renting.

Oh, and apartments tend to rent within a few days(!), so you'll have very short amount of time to make your decision.

Good luck!