Philadelphia...
In the city:
Philadelphia Record Exchange, 618 S 5th St (215.745.4151)
...(large collection of all types of music)
Book Trader, 7N 2d Street (215-925-0517)(great for classical)
AKA Music on 2d Street between Market and Race Streets
In the western suburbs:
Gold Million Records, Lancaster Ave (Rt. 30) in Bryn Mawr
Shady Dog Records, Lancaster Ave (Rt. 30) in Berwyn
.