Okay I live in Philly. The liberty bell is UBER LAME. It's small. There's not much else to see around it. Don't even bother.
Pats is slightly less nasty than Geno's - in both places the meat is very greasy and it is overpriced because it's a tourist site. They are cool to look at, but if you want an exceptional cheesesteak then you want to go to Jims on 4th and South. The line there is jsut as long, and it has real philly people, not tourists. The rest of south street is kind of lame. There is some good cheaper food though:copa banana, right across from Jims, has great burgers, Lorenzos (3rd and South) has great pizza - $2 for a huge slice, but no place to sit. There is some other ghetto-ish clothes shopping, then lots of tourist type places where they sell corny t-shirts.
If you like artsy kind of stuff and good restaurants, go to Old City. Market st between like 5th and Front is the main drag of Old City, but it expands a few blocs north and south of there. It's where the fancy clubs are and the nice restaurants. There are lots of art galleries up on market. Also, this is the area where all the historic type buildings are. Ben Franklin's house is on 4th and Market i think.
Philly Museum of art is great - probably most visited museum in philly. Ben Franklin museum is alright, but is more geared towards kids with interactive type exhibits.
I don't know if your 1 day includes a night, but if you want to go out for some drinks you can go to Old City for the classy side of things, or if you want a real unique philly experience, check out McGlincheys on 15th and Locust st. It is totally classic - probably hasn't changed in 40 years. The prices seem like they haven't either - a pint of rolling rock is $1.35 I believe. It's always an interesting crowd too. Also Continental on 18th and Chestnut is pretty outrageous for both food and drinks. It is a really fancified diner with EXCELLENT food for all meals. It is also great for going out - it has outdoor seating on the roof, like 3 or 4 bars, and a pretty classy clientele.