Wow. Quite a variety of opinions on some of these headphones!
As for my own collection, I think it's best to rank them by how frequently they get used. Obviously, this isn't perfect, but then what is?
Senn HD 600
Senn HD 800
Beyer DT-48 (circa 1960)
I've been debating buying one really high-end set of cans, but I'm not quite convinced I would get much more out of them. Given my system, I'm not sure the headphones are always the limiting factor. And I really like the sound from some of the older headphones....