Noise canceling headphones use cool technology to fight back against the constant problem of background noise, whether it's a co-worker who constantly clears her throat or the drone of a jet engine when you're traveling. But the best ones (like the Bose QuietComfort2) are bulky and expensive. You could construct your own for cheaper, but an easier alternative is to get some top of the line, comfortable earphones that act as earplugs but still allow you to listen to whatever you want. (If you don't need to hear anything at all, just get some good earplugs to begin with. This Slate review is a good place to start.)
The company that's known for making the best earphone/plugs is Etymotic, which makes several versions of its Isolator earphones. The 6i version—made especially for portable devices like iPods—is compact, comfortable, and is selling for just $75 at Amazon. Not quite as hi-tech as noise cancelers, but they do pretty much the same thing.