Originally posted by: snes tor
why a hundred dollar set of headphones?
Because its worth it.
OP: How do are you going to be using these headphones? If you need isolation and portability, then the HD280's will be a better choice because they're smaller than the HD555's and sealed. If you're just going to be using them around the house, then the HD555's will give you much better sound quality for the money. They're also supposed to be very good for gaming, if that matters to you.
If you can give me a better idea of what you'll be using the headphones which, I might be able to come up with some other suggestions. I'd also suggest checking out
http://www.head-fi.org to get advice from people who know much more about headphones than I.