Rodin Museum is a must see for art fans.
Dante and Luigi's restaurant if you are feeling spendy.
Eastern State Penitentiary is an amazing ruin for history fans.
But if you like beer, this is the place to be. Just some of the many excellent beer bars:
St. Stephens Green
The Sidecar Bar
There are tons more. And if you are planning a visit, you can do it during beer week Philly Beer Week 2011 * June 3 - 12
Sure, get a cheese steak. Better yet go to Isgro's bakery or Termini Brothers and get a cannoli, but don't forget to stop by some of the amazing bars. You will find local and craft brews in some of the least expected watering holes.