What's The MLS? Multiple Listing Service is a regional organization that collects and distributes data about homes listed for sale by licensed professionals.  The MLS in Silicon Valley provides selected information though its own service (below) and to many other sites which brand  in different ways.  MLS Listings is the most complete and reliable public information resource for local real estate.
Non MLS sites provide another option for selling homes without the MLS (see Search Galore).  However, either indirectly or directly most of the listings displayed are MLS based.
You Should Know searching the Internet (like driving neighborhoods, and pouring over newspapers) rarely results in acquiring the best home values.  By the time you get through all the facts and obtain the information you need to make a decision, the hot property is sold (sometimes before the "for sale" sign goes up). In the bay area market successful real estate hunting is done with an agent who has the experience, resources and methods for monitoring the market proactively for your specific needs.