After I finished this, I thought others might find it helpful.
I went through Ancestry's card catalog for PA newspapers and listed the towns in which the newspapers were published. Towns may have more than one newspaper cataloged on Ancestry, and the papers vary by date.
My goal was to have a map I could reference when I know a the location of an event, and need to know what nearby newspapers Ancestry may have available.
The result is this map:
View Ancestry PA Newspapers in a larger map
EDIT 8/1/2010: I should mention that I don't work for Ancestry, and Ancestry isn't affiliated with this blog in any way.