Multi-family Property Owner Lists

[Andrew Bosworth]

This has probably been discussed elsewhere at some point, but what are some resources you would recommend for finding lists of property owners?  In particular multi-family properties? 

Where I live (Harrisburg, PA), the local county tax maps provide a lot of information, but they are only useful if you are already aware of a particular property.  I am looking for a tool where you can enter your search criteria, which will then compile a list of properties, owners' addresses, etc.  -- preferably a free or pay-as-you-go option, versus a subscription service.