Huge cosign on Armstrongs, but be hungry. We used to order from there every Friday when I worked at Pittsburgh Airport, I would imagine the menu has changed some since 1997/98 but I ate just about everything on it back then and don't recall ever being disappointed.
If you are looking for a more casual/family atmosphere, Armstrongs was always good, and has a huge selection. Its across from the police station in the plaza.
For Italian, Marios is just up the road (Beaver Grade Rd) from Armstrongs towards the High School.
If you are staying near the airport, you are more then likely in Moon Twp. There is a Primanti's on University Blvd in Moon. If you can, the original shop in the strip is worth it for the "ambience" alone, but if you are transportationally challenged, the sandwiches are close to as good at the Moon location.
Pittsburgh has some very good and unique pizza places that are all worth a try depending on what area you are in. I'll run you through a handful of them.
If you get stuck in the hotel, Angelia's is the delivery place you want in Moon. Its solid pizza, nothing over the top but good. They also offer a sandwich called "The Pig" that is quite an adventure, and their other hoagies are also good, not sure if things are the same but back about 10 years ago they were using fresh Cellone's rolls for everything. If you are in their delivery area, your hotel will have their menu at the desk. If you order a chicken or steak salad, be prepared because it will come with a mound of shredded cheese and hot french fries on top, this is how most Pittsburgh places do them.
Franks Pizza on Duss Ave in Ambridge (about 20 mins from the airport) is a pizza place a lot of people rave about, some claim the best in Pittsburgh. Its not my favorite but its good, they cook with the cheese on first then sauce on top which is what sets it apart.
Police Station Pizza (actually called Pizza House) is also in Ambridge, they serve a traditional Sicilian style pizza which is one of my favorites in Pittsburgh. Its not for everyone, but if you are a bread/crust fan, this is your place.
Beto's in Banksville (just outside downtown) is also Sicilian style, but a less hearty crust. The thing Beto's is famous for is the cheese is put on the pizza after its cooked. It sounds weird, but it is actually pretty damn good. By the time you are eating it, you have the bottom layer of cheese kinda melted, but then a mound on top that is still cold. The first time I was their I almost walked out, but after going to high school nearby it grew on me and is now one of my favorites in Pittsburgh.
Fiori's Pizza is in the Brookline area, also just outside downtown. They do traditional round pizza, but their sauce is more on the sweet side If you've every had tomato pie in Philadelphia, its comparable to that style sauce, not quite as sweet but almost. You can also order extra shredded uncooked mozzarella on the side to throw on the pizza here too without being looked at like you've got 2 heads, though the pizza here is cooked with cheese like normal. Very, very good pizza either way.
Mineo's has historically been the top spot for a lot of people in Pittsburgh, the original is in Squirrel Hill but there is also one in Mt Lebanon. Their crust is probably closest to NY style, though thicker, it has that crispy yet chewy consistency. They also manage to pile an enormous amount of cheese on their pizzas, I think I've heard close to 2 lbs on their large.
Pittsburgh is also kind of known for its Eastern European population, especially Polish, and some of the comfort food from that region.
The Bloomfield Bridge Tavern is a dive bar through and through. You will get a taste of what Pittsburgh and its people are about here, and they serve classic Polish staples, perogies, haluski, kielbasa, etc. Check their website for hours as I think they may still not be open during the day or even on some weekdays.
The Church Brew Works is right down the street from the BBT. Its a nice, casual brew pub with great food if you just want to have a casual sit down meal and some beers. It is an old church, hence the name, and it is a really cool sight to see the conversion and all the brewery stuff inside there now.
If you want a romantic meal with your significant other one night, the Hyeholde is Moon Twp near the airport as well, although its a bit hard to find if you don't know where to look. Check the website if that interests you, I've never been there so I can't really comment on it.
If you think of any specifics or know any areas you will be spending time in feel free to throw it out there and I'll see if I can help. Have a great visit.