Jaime and Jim are right. Trulia, Zillow and Craigslist are all good websites. But if the advertized rent is too good to be true, usually it is either a scam or the owner is not paying the mortgage in preparation for a shortsale/foreclosure.
In the former case, the scammer usually copies an actual photograph of a legitimate advertisement (say on Trulia) then posts the same ad, often using the same words at a far lower rent say on craigslist. When contacted, the scammer will say that he is out of town and after some proforma qualification, will ask the prospect to wire money or send a money order to him, to get the key.
This happens all the time, and it recently happened to one of my clients.