We stopped at the Oklahoma City Memorial a couple years ago. I have to admit to some serious melancholy during the visit. The Field Of Chairs was particularly stirring to me. And my family was moved by the tour through the museum.
I strongly suggest a visit if you have time in the area. Easy on and off the freeway.
I've been to other memorials. Most notably the Arizona memorial, the Vietnam memorial, Ground Zero museum in Nagasaki. I've been moved by each and every memorial in some way.