There are a few places I have wanted to visit:
The Grand Canyon, obviously...how can anyone not want to visit such an iconic landscape?
Niagara Falls, for the same reason
Ground Zero: Having seen so much footage of the attacks and the aftermath (both immediate and long-term), I have wanted to visit the site to pay my respects and to get a more personal sense of it all.
The Bonnneville Salt Flats in Utah. As a massive automotive fan, I would love to be able to visit the site of so many Land Speed Records (even if there isn't much to actually look at)
I'd also like to see any forest that has Giant Redwoods....you can't really understand the size of those trees without seeing them in person.