My $0.02. The Bose QuietComfort 15 (over-the-ear, closed, noise canceling) are fantastic to code with. With no audio playing, low bassy sounds are entirely cancelled out unless extremely loud. Highs are reduced in volume, but still come through. Add earplugs and the highs almost go away too. Lastly, turn on some music or pink noise and you're not going to hear a thing.
Bah, real hackers make their own (passive) noise canceling headphones :) Here's mine: http://media.aeminium.org/~slug/2008/headphones/P1010608.JPG For $18 + headphone speakers, can't beat the price. Worked so well I made two to keep at different locations and also carry one when flying. There's an instructable too http://www.instructables.com/id/Jackhammer-Headphones/ The difference to mine is that I drilled a hole t…
They're less comfortable to wear since they squeeze your head harder than headphones (maybe I could adjust mine by stretching the metal headband with two vice's or something), and they have a bit more weight. But for $20 instead of $300, and hack factor, you win hands down! :)