If you want to experience one of the coolest atmospheres in Pittsburgh and some awesome beer, I'd highly suggest Voodoo!
I waited to judge Voodoo until my second time here, and I gotta say, it still held up to my expectations. The building is located in a cool old police station, and decorated in the coolest chalk art I've ever seen.
With an assortment of beers on top from Voodoo, you can't go wrong. They have something for everyone here. The customer service was even better, when I ordered my beer, they just kicked the tap when the bartender opened up a bottle so I didn't have to wait for a new one. Applause to you, that impressed me more than anything.
On a Friday / Saturday it does get crowded, so I would get there early if getting somewhere to sit is important to you.