Sony MDRNC8/BLK Noise Canceling Headphone, Black

Compared to nothing (in the way of noise cancelling) these are better than that.
Damning with faint praise?  Yeah, I guess so, but really what can you expect for the price.
Sony makes a product that generally is worth buying, if it meets your criteria.
If in this case the criteria is cheap, light weight and easily portable you are in luck.
If it is for noticeable noise reduction, again you are in luck.
If you have any pretensions of being an audiophile, and getting high quality audio, well, that's not going to happen.
These do offer some noise reduction, and being on ear, as opposed to over ear they really can't isolate much. 
I would say, bump your budget up to closer to, but still under $100, and you can find much more effective noise reduction, as well as better audio.
These are barely acceptable, and then only for non-discerning listeners. One feature I appreciate is the use of a replaceable AAA battery. And the long life these give using that one battery.

OK I have not had these only a few days. But my first impressions are cheap, OK sound quality, worthless noise reduction and about what to expect for $40.00 headphones.
I like the sound, its not breathtaking by any stretch but its OK for a laptop or iPod. The construction is nice for travel. The ability to fold them up is nice. But the plastic does not impress me as being something that will last getting tossed around.
The noise reduction is a joke, when I first turned them on I instantly heard a hissing sound. Very faint but pronounced with no content playing. I tried several different types of music and was happy with the sound but as for reducing background noise. I could not tell any difference with the reduction on or off. Actually the design of the headphones reduces noise passively very well. I also felt the headphones were a bit on the quiet side having to raise volumes to max on my laptop. Could be just a miss match with my laptop.
I am not disappointed but not thrilled with these, Maybe noise reduction is better with low frequency noise like on a train or airplane. Sony has a disclaimer on that. Saying higher frequency noise like talking will not be affected as much. If your really into noise reduction my advice is look elsewhere. If you need a step up for portable music player. Then I recommend them.