There are thousands of pairs of headphones on the market, but only a fraction are suitable for DJ'ing. The main points to look for when investing in a pair of headphones for DJ'ing, regardless of budget;
Closed Back design - these are the headphones that cup around your ear. This design helps block external noise so you can clearly hear what's coming through the headphones. Absolutely essential.
Detachable, single-sided cable - where the cable is connected to just the one earpiece.
Brand Name - You can get cheaper imported versions of most of the recommended pairs of headphones below. However, they won't sound nearly as good (bass response will be practically non-existent), and will feel flimsy so you'll be getting a replacement pair in a few months. There are reasons why the likes of Denon, Pioneer, Sennheiser, etc have become leaders in their field.
Other 'nice to have' features in a pair of DJ Headphones include a foldable design, carry bag, and coiled cable.
Recommended models are below (The prices quoted are as a guide only, and any links to external sites were correct at the time of publishing); Budget (Under £50) Sennheiser HD215 Sizzla says; "They come highly recommended, good sound quality, robust build especially for us travelling DJs……..we tend to knock our equipment about and lend to fellow DJs that occasionally forget theirs. They are very comfortable to wear, can be worn for long periods without discomfort. They have one swivelling ear-cup for side listening and to create the authentic DJ effect!!! They have a detachable single sided cable, parts are readily available." £35.99 - iHeadphones.co.uk
Sony MDVR700 DJ Melody's current weapon of choice. They've been around a while and are a firm favourite with many dj's due to their high performance and looking the part. The only downside with these, from other users, is the plastic hinges which don't take particularly heavy use. You can get round that by just looking after them!! They do generally retail at around £70, but you can pick a pair up for less if you look around. £69.99 (free delivery) - play.com
Sennheiser HD25SP These were my tools back in the days when I used to dj house music. Really robust and great sounding. The cheaper version of the HD25's, they don't have 'the look' of some of the big chunky silver 'phones, but have better build quality than 90% of the models out there and can really take a battering. Sound quality is as good as it gets. £67.99 - dv247.com
Denon DNHP700 (£99) & DNHP1000 (£109) Borrowed the DNHP1000's from another DJ at a recent gig. Very very good. They're extremely sturdy, comfortable to wear, loud and sound good. The DNHP700's have only recently been released in the UK - pretty much the same specs as the 1000's but in black. They're on my shopping list!!
DNHP700 - £99 - htfr.com
DNHP1000 - £109 - htfr.com
Pioneer HDJ1000 Along with the above Denon's, these are the holy grail of DJ Headphones. These are Sizzla's main pair, so what more endorsement do you need! £119 - chemical-records.co.uk
Sizzla says; "They come highly recommended, good sound quality, robust build especially for us travelling DJs……..we tend to knock our equipment about and lend to fellow DJs that occasionally forget theirs. They are very comfortable to wear, can be worn for long periods without discomfort. They have one swivelling ear-cup for side listening and to create the authentic DJ effect!!! They have a detachable single sided cable, parts are readily available."
DJ Melody's current weapon of choice. They've been around a while and are a firm favourite with many dj's due to their high performance and looking the part. The only downside with these, from other users, is the plastic hinges which don't take particularly heavy use. You can get round that by just looking after them!! They do generally retail at around £70, but you can pick a pair up for less if you look around. 
These were my tools back in the days when I used to dj house music. Really robust and great sounding. The cheaper version of the HD25's, they don't have 'the look' of some of the big chunky silver 'phones, but have better build quality than 90% of the models out there and can really take a battering. Sound quality is as good as it gets.
Borrowed the DNHP1000's from another DJ at a recent gig. Very very good. They're extremely sturdy, comfortable to wear, loud and sound good. The DNHP700's have only recently been released in the UK - pretty much the same specs as the 1000's but in black. They're on my shopping list!!
Along with the above Denon's, these are the holy grail of DJ Headphones. These are Sizzla's main pair, so what more endorsement do you need!