Where Should I Take My Metal Detector In Western PA

You need to talk to local people. Ask your parents and grand parents if they are still alive for good spots.
Any place that used to be a picnic area, an old swimming hole or an old time circus area. Around Churches, Granges, Masonic Lodges, parks whatever. Any place where the is a really large and old tree I would go metal detect under it.
Take a look at this: http://en.wikipedia.org/wiki/Sanborn_Maps
If you have these maps in a local library you can get copies of them and then load them into Google Earth as overlays. Lets you pinpoint old buildings, etc.
Go to the library or histoical society and find old maps for your area.
Any place where people congragated is an area where things could have dropped.
I am out West so things are a lot different. But I look for old Wagon trails, CCC camps, old homesteads in fields (usually found by a stone foundation or broken pottery and glass), tent revival meeting areas, trading posts, old schools, ferry landing spots, old military forts (the west is littered with them), stage coach stops, mining areas, etc.

Just make sure you have permission on private property. Check your local laws for public parks in the cities too. Some areas you will need a permit, some areas you can't metal detect. Remember, historical monument areas are a no no.

Chz,

I'm up in Erie, send me an email, interested in your exp. just got my md, and am thinking same thing as you.