The real problem with broad, unspecified requests for attractions to visit is that following such a list, and there are plenty of them out there, is that following them will almost certainly result in a less enjoyable trip. The problem is simply logistics. If a site is a generic 'must see', that means that every tourist in the area must see it and that site will be overly crowded, your photographs will be full of other people and traffic will be horrendous. It's certainly possible to see popular tourist attractions without too many tourists by time shifting. For example, I saw old Faithful erupt with a grand total of 0 other people because I went in October rather than August. The other way to avoid a tourist crunch is to go to other nearby locations and parks that are just as memorable but not on the lists. The two locations where this is most evident are Mount Rushmore (where the 'other' locations include Wind Cave, Jewel Cave, Devils Tower and the Crazy horse Memorial) and the Grand Canyon (Walnut Canyon, Sunset Crater, Wupatki) but Yellowstone also has other National Park Service and State Park locations nearby, just not as near as those listed above. These include Craters of the Moon, Thousand Springs, Fossil Butte and Bighorn Canyon. So just widen your horizons a bit and you'll likely have a more enjoyable trip.

AZBuck