[jcranmer]

Probably most of them; it's more the case that a few of the National Parks are just too overcrowded--Shenandoah and Yosemite probably the worst of the lot. Although some of the National Parks do have issues that aren't related to overvisitation (Hawaii Volcanoes and Everglades both come to mind).

[bombcar]

That's basically it - someone bandied about a statistic that visitors to National Parks on average don't get more than 50 yards from their car.

So if you want to see natural beauty, be willing to rough it a bit and go were people don't.

Of course, the most popular places are considered the most "beautiful" but that's not entirely true - and the popular places you can watch documentaries on.

[QuarterReptile]

It's funny to mention Shenandoah. My experience is maybe 10 years old at this point, but I don't think I've ever been to a less crowded national park.

[derwiki]

You should check out Canyonlands sometime!