Headphones

I think you know what headphones are. They need little explanation.

Popular models (price order)
Koss Portapro - $30

AKG K81 DJ - $40

Sony MDR-V6 - $65-80

Grado SR60i/80i - $80/$99

AKG K240 Studio - $93

Beyerdynamic DT770 - $170

Audio Technica ATH-M50 - $199

AKG K702 - $245

Beyerdynamic DT880 - $270

Denon AHD2000 - $300

Sennheiser HD650 - $350

What should I do
Aside from going to a store, using your ears and trying the headphones you can use the graphs on this site:

http://www.headphone.com/learning-center/build-a-graph.php

And learn what they mean with their guide to headphone statistics:

http://www.headphone.com/learning-center/about-headphone-measurements.php

Please bear in mind that these graphs can not accomodate things such as comfort, looks and the padding the headphones have (think about it, wearing leather pads for an hour, combined with loud music, can make you sweat - velour pads are much more suitable). Also you shouldn't be worried about looks, unless you are maybe considering some headphones for public use (in which case you aren't worried about sound quality so much as isolation).

Beats, Bose and Skullcandy are not worth it.