For guitars, I dealt with Acoustic Roots in Jenkintown, PA before Larry the owner closed his shop there and moved into his own section of the Medley Music store in Bryn Mawr, PA (though he still calls his own business "Acoustic Roots" for now). I haven't visited the new location since it's farther away from home, but I'll get there eventually. Larry isn't exactly a "people person" but he has an excellent reputation with instrumentalists. Here's Larry's page: http://www.medleynet.com/acousticroots.html

And, tucked away on a little side road, there's the Bucks County Folk Music Shop in New Britain, PA, which deals in guitar sales and repair, but also sells and services the harder-to-find folk instruments (including dulcimers, bodhrans, button accordions, etc., even bagpipes and boombas). Their site: http://www.bucksmusic.com/