Redeye VC: Deja vu has a nice write-up on Zillow offering "Make Me Move":

A homeowner can easily post a Make Me Move price without exposing any personal information. Zillow then enables interested buyers to contact the owner through an email anonymizer.

It’s a feature that I wish we had when my wife and I were looking for a new home. We knew - from driving around and around - that there were certain houses that we would be interested in. In retrospect, I wish we’d done the simple thing of leaving a letter on the front steps saying “if you ever sell ..”

Much simpler and also effective. My wife has a favorite rocking chair that she got because she was one of the first in line at a moving (estate) sale. The home was on a tour and my wife wrote them a letter saying “if you ever want to sell any furniture, I’d be interested”. Some time later, the owners were downsizing and we ended up with 2 lamps, a table and chairs and 2 rocking chairs.