Record Shops in Philadelphia

Hi folks. I've got a conference coming up in the city of brotherly love and was wondering if anyone can steer me to some quality record stores in the downtown area. Used (and new) LP's and used CD's are what I am after. Thanks!
In the downtown area:

Philadelphia Record Exchange would be my first recommendation, but they've been closed every time I've been by in the past 2 months: on 5th Street, one block south of South Street.

Repo Records
538 South Street

AKA Music
2d Street, a block north of Market

Russakoff's Used Books
10th Street, between Locust and Spruce