Arguably the most underated peice of kit in a DJ's arsenal are headphones.  If you can't hear it you can't mix it.  You need a headphone thats comfortable, can fit & adjust around your jaw, has enough volume to be heard over the cranking PA, enough bass so you can dial into that kickdrum over the subs in the club and made tough enough to handle the punishment of being abused show after show.  Here at Kosmic we stock all the major DJ Headphone Brands including Sennheisser, Pioneer, Skullcandy, AKG, Behringer & more.