In addition to the ones BBE listed, I'd split the Rhoynar/Dornish group into separate categories. The orphans of the Greenblood are the closest to the original Rhoynish culture. The Dornish are described as having 3 different phenotypes--stony Dornish, salty Dornish, and sandy Dornish. This could correlate to different cultures (especially since, logically speaking, you'd expect people who live on the coast to have different lifestyles then people who live in the desert interior). The stony Dornish, being the ones least touched by the Rhoynar influence, would also be the most Andal in culture.
The are also probably weaker cultural differences between the Southern, Andal, kingdoms, the way you might have a Western European culture, but France and Belgium are still different. As we saw with Brienne and Nimble Dick, Tarth and Crackclaw Point have totally different bedtime stories. And within the kingdoms, there are probably regional differences too, in food and dialect, just like in the Middle Ages here. It doesn't affect the nobility as much, because they are educated by a common institution (maesters) and often travel and marry outside their borders. We don't have much POV from smallfolk, so the difference between a peasant from the Vale and one from the Dornish marches aren't described.
Also, the Skagosi are a separate culture that needs to mentioned. Other Northmen find them (and their cannibalism) creepy. The wildlings find them weird. I'm really looking forward to seeing them.