Headphones are a very personal choice, every persons ears are different. There is a difference between studio headphones and consumer headphones. Studio headphones are made to isolate you from your surroundings somewhat, and provide a very neutral almost dry sound. They will usually have very clear highs. This is so you can really hear what is going on with your mix. They are also made to be comfortable for long stretches. Consumer headphones are usually not that clear, have enhanced bass, and are geared to make the sound pleasant and more laid back in some ways. Most people listening casually will probably choose a consumer headphone every time. Pro headphones just sound less forgiving and more challenging.
Another thing to watch out for, is to avoid any headphone that has active/electronic noise cancellation technology. These change the sound of the music too much, applying electronic equalization and sound leveling you don't want when you are mixing.
Calling a headphone "Studio" really means nothing, it's just a marketing term that is very over-used in consumer headphones.
The Beats are really made for consumers, not the studio, despite what the advertising says. They are too colored and don't allow the fine details of your mix to come out. Beats tend to be bass heavy, and do weird things with imaging, and lose detail in the highs. Beats tend to be extremely overpriced for their performance, you can almost always find a better headphone for about 1/2 what they cost. However, I really like the Beats Pro, one day I want to find a pair used (though I would never mix with it).
One thing to keep in mind, if you get a headphone with enhanced bass (like a Beats) your mixes will actually probably turn out sounding thin and anemic, because your ear will be compensating for the headphones bassiness. Which is probably what you don't want.
I would suggest looking at Beyer-Dynamics, or maybe Sony as some people have suggested.
One headphone that is used A LOT in studios for pop, rock, electronica etc. is the Audio-Technica ATH-M50. It's a great headphone that is the best of both worlds in that it has great bass, and good highs, but still works good for mixing. It's very inexpensive for it's quality. It will run rings around most consumer headphones and wipe the floor with any of the Beats. So you will enjoy a headphone that is great for listening for fun, but also a serious tool for mixing. You can get them for about $150. One thing about them is that they fit pretty snug around the ears, so that they isolate well. Some people don't like that. They are very efficient which means they play loudly and clearly even connected to an iPhone.http://www.amazon.com/Audio-Technica-ATHM50S-Professional-Monitor-Headphones/dp/B004ZG9TMA/ref=pd_vtp_e_1