Have you tried a few different airports? Did you try Southwest from Philly?
Also, something I found just recently - out of PHL, sometimes you can book a nonstop flight on United that is really a codeshare flight with US Airways (ie, they put you on a US Air flight). We just booked a flight in November for $64 per person one way. A ticket through US Airways on the same exact flight was $120 per person.
Good luck!