NH and MA is of course a nonsense answer. Southern NH is basically the most affluent part of the Boston outer suburbia.
Lemme see...apart from the more obvious answers given as yet in the thread, can I come up with some other ones?
Indiana isn't as different from its neighbors as its voting history suggests...the components are basically the same, just the mix is different.
How similar are Iowa and Missouri? Iowa and Nebraska? Missouri and Tennessee?
Mississippi and Arkansas are in ways very different (one epitomizing the deep south, one the upper south, one long with a black majority, with a black pop. now long declining, one always overwhelmingly white, with a black population share not really fallen much, one with whites voting as a bloc, the other with the most Dem-friendly white population in the south), in others very similar (ie a history of poverty and cotton share cropping, only one dominant city)...
How about Oklahoma and Colorado?