My daughter told me about an iOS app called Visited States Map which lets you keep track of the states you've visited in the United States. You can color-code the the states if you want to show states you've lived in, states you have only been to when making a connecting flight at the airport, and states you forswear never to set foot in.
As far as I can recall, I've been to 32 out of the 50 states. Of the 18 states I have not yet visited, Alaska is at the top of my list. They thing that keeps me from going is my dislike of mosquitoes, which I've been told live in abundance there.