I went to an audiologist and paid $100 to have molds of my ears taken. A week later, I had a set of ear plugs with filters in them to block out most frequencies. I bought them for flying, and now that I have them, I would rather miss my flight than fly without them. If you're just looking for the noise silencing aspect of headphones, I'd highly recommend a custom plug.

For music, I have a pair of Shure E2Cs. They not only block out sound really well, but in my opinion produce very good sound. One big advantage of in-ear design like this is that you can significantly lower the volume of your sound source, which will keep your ears happy and healthy. But not everyone feels comfortable with the in-ear style. When I bought the Shures they were @100; today the Shure SE210s are available for $100, but I don't know their product line very well, so I don't know the difference, say, between the SE210s and the cheaper SE110s.

Also note that with most of the in-ear headphones, you can take them to an audiologist and get custom plugs made, as well. It's probably not worth it to buy a $100 set of headphones and then pay an extra $100 to get custom molds, but if I were purchasing a higher end set of Shures (or a similar product from Westone or Etymotic), I'd get the molds.