Shamrock, Texas has some nice restored 66 buildings - I recall the U Drop Inn and an old gas station. There’s also a replica of the big stone Texas-shaped Highway markers that used to indicate your entry into the state. I was born in TX, so have lots of family photos my parents took with the signs starting when I was about one year old.
Winslow, AZ has the “can’t miss it’” corner to stand on, with the giant 66 emblem painted on the pavement, and a great mural on a building wall. Nice store on the corner with all kinds of 66 souvenire doodads. As mentioned above, Homolovi State Park is nearby and a great place for some easy, interesting hikes.