I need a cheap headset that can block out ambient noises. In order of feature importance, I would rank it as follows: Noise cancelling, sound (I listen to mostly hip hop)/comfort, design, built quality.
It's a little bit more expensive but it is worth every penny...the monoprice 8323
Based on you preferences you won't find anything better for ~$30
Also here is a post comparing 3 budget cans.