when i moved to SF i walked around the TL and rang building managers of nicer buildings and asked to see what was available. in Boston the most up-to-date info was not online but in a steno book of a guy in a subbasement in the Fenway that connects to various buildings via utility tunnels, even getting to him required 2 elevator-trips and some stairs, but it really illuminated how things work. in between padmapper, hotpads, trulia, zillow and the exclusive broker-listings and MLS-shared rentals therein, as well as alumni-mailinglists/forums containing for-owner listings and carefully-crafted CL search-bookmarks and working with a couple human brokers it was possible to get a good sense of roughly everything in the market