I don't know of a place in SF but try Dream Hire, they ship all over the US. Although I think you have to rent for 4 days if you aren't in Nashville or NY.
Also in SF, there is a new studio called San Francisco Sound Works, I don't know if they rent gear, but I know they want to try and start a good community, so it may be worth a try to check them out. www.sfsoundworks.com