About DJ Headphones:
Headphones, once considered simply an accessory, have always been a necessary part of a DJ's toolbox. From queuing up tracks to matching beats, you need "cans" that stand up to heavy use in situations where they also need to be able to be heard above the outside noise of tracks being played and the crowd noise.
Most DJs use on-ear, or "supra-aural," phones, which rest, as should be obvious, on your ear. They don't offer the extreme isolation of over-ear, or "circumaural" phones, so they're a great choice when you need to be more aware of what's going on around you. Since they don't form a sealed chamber, they tend to have a more open sound with a frequency response that is very stable, so they're also an excellent choice for reference monitoring and headphone mixing. Because they rest on your ears, long sessions can get uncomfortable, which is why supra-aural phones with easily replaceable ear pads in a variety of foam density and covering types have become common.
Over-ear, or "circumaural," phones fit around your ear, creating a sealed chamber. Most really high-end phones tend to be of this type, as over-ear phones can fit larger drivers for better, more even frequency response, with a much tighter and more controlled low frequency response. Circumaural phones tend to be the most immersive listening experience and make excellent reference monitors, but some club DJs feel they remove them too much from what's going on in the room. Due to the fact that they're the largest headphones, they can be a little heavier, but modern materials have decreased that weight and made long sessions with over-ear cans much more comfortable.
DJs have considerations beyond just quality of reproduction and volume. Most DJ phones are designed to have one earpiece flip up, so you can monitor the currently playing track in the room, while queuing up the next part of your set, and also hear the crowd so you can interact with them more easily. There are a number of different methods used for this, so it's important to check that the method used on a particular set of phones will fit in with the way you like to work before you settle on a pair.
Phones can also be a showcase for style, and many new models include LED lights or other design elements to make them stand out. Obviously, sound should come first, but you've got some excellent choices if you also want to attract serious attention while you're spinning tracks.