I just wanted say hi and also chime in with my thoughts on living in philly (as I've been here for the past 5 years attending drexel and actually work in leasing in the city right now)
rent's have gone up significantly in cc in the past couple years; its difficult to find a deal now, your best bets are washington sq. west and the art museum in terms of decency of neighborhood and cost.
quick note about washing sq west- certain chunks are bad at night as they get turned over to drug dealers and transvestite prostitutes. Generally nothing happens to the residents, but its loud at all hours and your bound to trip over a condom or a pair of discarded underwear every once in a while should you live on/near one of the afflicted corners- 12th and pine is particularly bad.
queen village and the italian market are nice too but a bit harder to do trains fro, but there are lots of buses.
if you have money to burn old city, society hill and rittenhouse sq. are all great neighborhoods to live in, but generally pricy unless you find a deal (which does happen occasionally, my friend just moved into a 1 bd. for 1050 a month like two blocks off the sq)
I live in society hill and love it, but rent's here are ridiculous- only reason I'm here is because my landlord is senile (and rented the apartment way under market price when we first started renting) and hasn't raised the rent a dime in the four years we've been living here.
craigslist and phillyweekly.com are really the way to go if you want to find something in an affordable price range, particularly phillyweekly.
also if you find a place you like that you are ok with the price on, put a deposit down immediately, I can't tell you how many people I know have missed out on really amazing places and prices because they went home to think about it overnight, called the next day and found the apartment to be taken- it even happened to me a few years ago.
also here are some notes on areas I would avoid living in: obviously the area immidietly surrounding campus (that should go without saying at this point,) I would avoid university city as well, and fishtown/northern liberties might be nice in a couple years, but right now they are pretty miserable.
Personally, I'd also avoid manayunk/roxborough/etc., mostly because I don't own a car and they aren't exactly friendly areas to that lifestyle, but also because you really are quite removed from everything center city has to offer (which is surprisingly much and getting better everyday I think.)
On a random note: I'd also recommend philly car share to anyone who isn't bringing a car, I just started using the service and I love it, there are cars all over the city and its like $5.50 an hour.
Sorry for writing a small novel there, but I hope it helps anyone coming from out of town! I know I would have loved some of this info. when I came out here from chicago a few years ago.