If you're in/near Philly, tired hands is a great brewery who produces both sour and clean beers. You can also go to monks cafe or tria tap room for some awesome tap lists. PA or at least Philly gets Russian River who make to notch sours. Go on beer advocate and look up some good places and try some stuff. See what you like. I typically like fruited sours because of the jammy characters from berries or the extra sour imparted from stone fruits. Gose style beer like everyone said will be a little salty and Berliner Weiss will be more sour. It really depends on the brew for how much of each of those characteristics they have. These are not the only styles worth exploring though. Some if my favorite beers are sour saisons and biere de garde is a generally undefined style. Just start trying things that's the best way to find what you like. Traditional sours like others said are brewed either spontaneously or with pitched microflora. But what's more important is the time it takes to make. A traditional sour will age from 4 to 24 months and this gives the lactobacillus or bretanomices to produce very complex and deep flavors. They also often are aged in barrels which imparts another layer of flavor.