Philly is a great town for the performing arts. Broad Street is known as the Avenue of the Arts and is jam packed with theaters, but you'll also find them throughout the city. The Arden is a block from my sister's place in Old City and she and her husband used to have season tickets. They like to get season tickets to new theaters each year, but they told me the Arden was great. Check out their website to see what the current productions are and for more information. Tickets for individual shows usually run around $20-$30.
Dress Code: picture coming soon . . .