Earbuds are a no nonsense way of getting your music without the added bulk of full sized headphones. Sony's MDR-EX51 offering of in-ear earbuds are designed to seal off outside noise, while giving you rich sound and comfort.
At first, these earbuds look good. The simple black and silver scheme aren't too distracting and they won't get dirty. They come with three sizes of silicone earplugs, which you can adjust to your liking (I use smalls). The in-ear design puts them right into your ear canal, so it does a good job of preventing outside noise. This allows you to play your music at a slightly lower volume, but makes it hard to hear anything else (re: be careful when you're crossing the street!). I would classify them as lower end noise cancelling, but more expensive options from Shure and Etymotic will do a better job of 'cancelling'. The sound is good, the bass is deep for drivers that size, and a clear difference from the standard iPod phones I was stuck with.
The cord is designed with an around-the-neck style in mind. When it splits to each earbud, one side is much longer than the other, which allows for the extra length to wrap behind the head, keeping it out of the way. The end plug to the 3.5mm of your choice is a bent elbow, instead of straight, which should be of note. Although I enjoy this design, I did not find the cord construction to be any good. After a while of use, the rubber in the cord began to twist and catch on things, causing it to tear. This choice of soft rubber leaves the wires exposed and repair is a hassle. This problem develops over time, as you will not notice the change in the rubber until much later. This was a big problem, as it essentially leaves you with a broken set of earbuds.
Despite the good sound quality and aesthetics, the fact that the cord is a crucial part of a earbud design makes the MDR-EX51s not a very good purchase, even with its lower pricetag. Put your money towards another set (possibly the Panasonic HJE50s, which I've replaced them with and have reviewed) for a better long term solution.