http://www.amazon.com/Audio-Technica-ATHM30-ATH-M30-Professional-Headphones/dp/B00007E7C8

About as good as you are going to get for under $50.

$50 is good enough for solid studio headphones.

Right now, I'm wearing these Audio Technica m30s, cheap and the difference in audio quality is already very noticeable

If I were shopping again, I'd probably go for these Sennheisers, they look comfy but a bit bulky. They don't list specs to purchase with caution