Noise-reducing headphones are wonderful for making music sound better in noisy environments, such as on airplanes and when lawn mowing. You can spend $100 or $500 for fancy ones, such as Shure's E5c Isolating Earphones for US$489.67, but Koss has a nice set for about US$20, called "The Plug" earbud stereophones.
The Plug's ear cushions, however, are a bit large for my ears (which suffer from being smaller than most earbud headphones), and tend to slide out when I move.
Last night at Wal-Mart, I noticed a pair of Excel CD101 earpads for CDN$5 (about US$4). They have a different design than the Koss. They fit my ears better, stay in, but suffer from lower quality sound -- the bass and high end are missing -- despite the enthusiastic "Enhanced Bass" claim on the packaging.
I can't find a reference to the CD101s on the Internet, but in a brief listening test, my daughter proclaimed them to be "pretty good."