I have a Facebook page for my window cleaning service, and occasionally post on it. On top of this, there is a local Facebook 'Do you know' page with 16000+ members. I used to respond when someone was looking for a window cleaner but I don't bother now. A number of my customers are also on this page and put my name out there for me when they see the post. More often than not I get the job because my name often comes up more than others. It's local, it's free, and requires no effort whatsoever on my part!
John