Time and again I ask what are rental prices are like in San Francisco, or in a particular neighborhood or size range. I almost always send them to Craigslist since it seems like that every rental listing shows up there. But wading through Craiglist isn't all that easy. With all the mashup technology someone, sooner or later, had to come up with a map based search... and sure enough someone did.
A new internet must is Mullinslab2.ucsf.edu/SFrentstats
Click on "2BR" or whatever segment you're interested in, and the map pops up, and from there you can drill down into neighborhoods. Or you can click on "Neighborhood Data" and see rents and total rentals by neighborhood. Or look at trends over time under "Overall Stats/Notes" for "Graphs of rent over time".
To me the best part, especially if you are looking for San Francisco rental properties, or if you are looking to buy a Condo or house to then turn around and rent, you can see the Craiglist rentals in a much easier to digest way.