Well, I live in Fairmount (near the Art Museum) and while it's very close to Center City, the subway does not connect with my neighborhood. For me, the bus is a great solution. Operated by SEPTA, the bus is $2 a ride and offers service all over Philadelphia. Check out the site below for a complete schedule.
There is a real Subways system in Philadelphia, but in the western part of the city there is still extensive street-running.