All the things drcossack mentioned are good.
I've never been to Ralph's, but I know the whole Italian Market area has some good food.
Citizen's Bank Park is an awesome place to watch a baseball game. You'd have to get your tickets on Stubhub, as we've sold out every game since sometime in July of '09.
The hotel he mentioned is definitely in a nice area, but it's kind of far away from the Convention Center. The mall nearby is huge, if you're into that sort of thing.
There are plenty of hotels in and around the Convention Center, so you shouldn't have trouble finding a place to stay.
Some other places of interest include, The Franklin Institute, The Please Touch Museum (If you are bringing along little kids), and The Philadelphia Zoo is always nice.
If you're looking for a good cheesesteak, DO NOT go to Pat's or Geno's. The only people that get cheesesteaks from these two places are tourists and drunks at 4 AM, since they're one of the few places open.
Instead, go to Tony Luke's or Jim's Steaks. Tony Luke's also has some great Roast Pork sandwiches (Get them with broccoli rabe and provolone).
The Reading Terminal Market is America's oldest farmer's market, and has a bunch of options to choose from.
I could go on and on, but you get the point. As I said before, if anyone has more questions, I'd be glad to answer them.
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