Not my experience, but driving for dollars seems to work. Finding Mom & Pop landlords with listings on Craigslist seems to be another good way to go.
I have created data scrapers before for auction listings and sites with atypical listings. That can be a good strategy, but there is a lot of volumes to wade through.
@Benjamin Brajovic Developing deep relationships with broker and property managers. You have to be in front of them at all times - lots of shaking hands and kissing babies. But they specialize and have developed networks which will greatly expedite an investor's progress.