Must have at least 1 extra movement possibility compared to normal consumer models (for instance rotateble or swivel earcups).
There goes the HD25.... no swivelcups. That, along with the fact that i agree with barthawk that the cups are too small, is the only thing that stops me from going out and buying myself a pair. The main advantave of the HD25 is that all parts are sold seperately, so if you do manage to bust something (which you'd have to try seriously hard for, or be a complete idiot) you can replace it instead of having to go out and buy yourself a new HP.AKG headphones
are generally quite strong as well, although i've never tested their new K181 DJ Headphones...