Headphones come in a variety of styles to accommodate various applications. I will offer information so that you can decide which headphones suit you best.
For recording application in the studio it is best to find a pair of headphones that are both noise canceling and have enough power to generate sound over what is going on in the studio. The most common are the closed back headphones. They have tight coverage around the ears and minimize any leakage from outside sources. There's nothing worse than recording an incredible vocal take only to discover that the click track has now leaked into it. For recording applications my pick is either the Sony MDR 7506 or the AKG 270.
Step2
For more hi-fi applications the open-air style is preferred. These headphones are not suitable for recording because the headset speaker design allows sound to be emitted to the outside world. It is very similar to the bass ports on a subwoofer or full-range monitor. If you cover them the sound will remain trapped inside and become very boxy or boomy. I have an affinity for the Sennheiser HD600. Though more expensive they are amazingly detailed and deliver a very accurate interpretation of the original sound. I have even mixed music on these. I use them all the time for either casual or critical listening. They are very pleasing to the ears and in no way fatiguing. They work very well with the iPod as well.
Step3
Choosing the right pair of headphones for the job is paramount and keep in mind that neither style works well for both applications.
Tips & Warnings
Generally, the closed-back design is much less expensive than the audiophile open-air style.