Some above mentioned checking the GIS. That has been the first place i looked after driving by a house. That should tell you any out building that the county is aware of (i.e. permitted), along with a general plot size and map of it. best of all, it will show what the taxes have been in the past, along with the assessed amount for many years. in my area, it will also tell the owner and where the owner lives- if its different from the listed address, out of state means a multi-property owner, in state/local means that they just moved and left the house. of course, not accurate for EVERY house every where, but around here it generally does.
as for searching MLS and sites like that, most of the houses i have found have not been on those sites. i drive around and look for empty houses or unkept yards. those have typically been foreclosed and haven't hit the market yet. searching the GIS fills in roughly how long they have been vacant (as shown by who pays the taxes (here, foreclosed homes have the same payer)) and if it will be going to market soon. my wife and i have had our eye on a house for 2 months now. i found it a monty before it went on market, so we saw everything that need to be done to yard and buildings before the bank put a band-aid on everything in order to list it.
