Yesterday I watched this three-part series on the accents of English-speaking North America:
The videos are by dialect coach Erik Singer and, I must say, his ability to fluidly move through all of North America's accents is incredibly impressive. As I was watching the videos, I kept thinking to myself, "I don't know what this guy actually sounds like when he's not putting on an accent."
The interesting thing about accents is that they really speak to settlement and migration patterns. In other words, who came in contact with who, and who didn't come in contact with others? Geographic isolation also leads to unique accents.