in no particular order, Costner, Duvall, Selleck, Eastwood, Wayne, Elliott, Russell, and his old man (EDIT!!!! I was mixing Kurt Russell from Tombstone, and Michael Douglas from Snowy...)(the Man from Snowy River is one of my favorites).. I'll come back to this with an edit.
On a side note, the casting of the players for Hell on Wheels, couldn't have been any more perfect.