In a couple of weeks I'll add ID and MT, which will leave only AK, HI, WY and NE.
I'll almost certainly hit the first three within the next couple of years. I think I'll make it a point of never visiting Nebraska, though; it seems more intriguing than to say you've done all 50.
Then there are the Highpointers, who attempt to visit not just each state, but the
highest point in each state. I'm a casual Highpointer (not too serious about it)and have 12 so far. Their site is at
http://www.americasroof.com . There are also "county highpointers" and "lowpointers".
I agree that changing planes in an airport doesn't count as being in a state. Someone once told me that he couldn't count Ohio yet because he'd only been in the Cincinnati airport... you better believe you can't count it in that case!