I've had no vacancy for two years; before Zillow purchased Postlets. When I did discover postlets, I quit putting signs in my front lawns, and had tenants sign contracts sight unseen, from half the US away.
I'm hoping it hasn't gotten as bad as I've heard, because I found it invaluable. The ability to post to one site, and have it distributed to all of the major renter search sights was spectacular marketing.
My policy, however, and how I end up getting most of my tenants, is by direct contact. Since my wife and I make more in rent than we require for our lifestyle, we are able to work any jobs we want. I'm an trained nuclear mechanic and dropped out of my civil engineering degree during my senior design project to begin investing. I enjoy working thought, as does my wife. But, the jobs we usually take are the types that our tenants also work.
They know that we are landlords, and good ones, so when they are looking for a place to live we are the first people they look to. The only problem, is that I never have any vacancy. I'm usually under a rental contract a month before my current tenant moves out. I'm not sure if that is just because of my local market, or the type of landlord I am. I do give a 10% discount in December so my family tenants can do a little more xmas for the kids.