[Garp]

Another European view here:
Cities:
New Orleans, went there prior to Katrina. Very enjoyable.
Seattle in summer is great.
San Diego, could easily live there. in fact it's the city/area which is often mentioned when I talk with colleagues about really nice places in the US.
San Francisco, at least some areas.
Some have mentioned Las Vegas, got married there, went back last year and I couldn't get out of there fast enough.
Landscapes:
Grand Canyon, been there twice, once empty, once very crowded, always enjoyable even with a distinct fear of heights.
Bryce and Zion, been a while but have very found memories.
The larger Sedona area, did some hiking there, very sweet.
Olympic Peninsula and the Puget Sound, love the area, the many historic forts and the splendid vista's.
Joshua Tree, had to see this, wasn't disappointed.
Kings Canyon, incredible impression.
The Natchez area, the plantations have a very special atmosphere, mint tea with bourbon. Oh yeah.

All of the above qualify as world class, I'd cross the ocean again to go there and I would recommend it to friends.