well I am sure there are going to a lot of answers depending on what you are looking to do but one starting point is paying for access to the mls. Then a free site is the county assessor site that shows the property zoning and some other info. There is also CoStar which can be worth it. ProspectNow is one that you can find some raving reviews on and it is pretty accurate gives property info with contact info which is generally pretty good.
But I would also suggest building relationships with asset managers who have long lists of properties in all asset property types. Remember real estate is just as much relationship based as it is direct mail or door knocking or internet searches.