I've got myself a master plan. A foolproof master plan. Here's the ultimate five step plan to finding housing in San Francisco. Use it with caution, as it may result it having to pay rent.

1. Come up with your criteria: Under $2000? Has to allow cats? Laundry on premises? These are things you need to know. If you're living with someone else (or moving in with them because you're tired of leaving your cat all alone when you're over at their house) talk to this person about his or her criteria. Since you're in a healthy relationship, hopefully the lines of communication are already open.
2. Focus on a few neighborhoods: Chances are that there are going to be some places you can afford to live but won't want to and some places you want to live but can't afford. Best to get that out of the way before you get much deeper. Head on over to HousingMaps.com and visit San Francisco. You can pretty quickly scan and see what it costs to live in different neighborhoods. You might enter you criteria from step one to make the job easier.
3. Make it a daily habit: The best way I've found to do this is to grab a feed from Craigslist. After you search, according to your criteria and in the neighborhood you're excited about and can afford, Craigslist will generate an RSS file for you (visible as an orange icon in your addressbar if you're using Firefox, which you should be). Throw that link into your feedreader and check it daily along with your favorite blogs.
4. Check the place out: Virtually, of course. From your feedreader, you can jump to the Craigslist post and then jump to Google Maps. You might as well jump all the way to Street View and check the street out. Is it where you thought? Maybe take a virtual walk around the block, looking for cool coffee shops, laundromats, or peddlers of assorted sundries? Does it feel like home? Or, more importantly, does it feel like bothering to call for a viewing? Yes, even I like to actually visit the place before I move in.
5. Staying connected: It's important to me that wherever I live has pretty good access to mass transit. I don't know why I love mass transit so much, all the diverse faces and personalities, each with their own exciting fashion and smells—all with the same iPod earbuds. It really gets me. At any rate, the official MUNI maps might be helpful. Of course, if you're more of a bicycler, walker, or excited to get a pair of his and her matching electric scooters powered by your residential solar panels and zoom around the city like Italy in the 60s... You should check out the SF Bicycle Coalition Bike Map & Walking Guide.

That's just what I've picked up so far. It's been working for me. Of course, I've only just recently started looking and haven't actually found a place yet... but not for lack of finding possibilities. It's just that sometimes they forget to mention that the bathroom has a brick wall in the middle of it or that they've used four different kinds of tiling for each room or that the house was built before refrigerators were invented so it sits in the middle of the living room. Stuff like that you can't enter into Craigslist searches. As my friend Brianna mentioned the other day, "Each time I post an opening for a roommate, I have to add more things that I would've never thought I had to put in a roommate ad—like, please don't cook kimchi at 4am."