I don't use headphones, usually, but rather earphones. My current pair are Philips SBCHE590 - in ear phones that supposedly give the sense of surround sound (they're quite good). They cost £15/$30.

My last pair were a pair of really high quality Sony earphones that cost about £50/$100.

So I could probably see myself spending quite a bit for some really high quality earphones.

Speakerwise, the best I have is my Creative 5.1 set hooked up to my computer which cost aboyut £40/$80.

Since I use earphones/speakers for a large part of the day (about 3 hours for earphones, and 6 hours for speakers) I'd be prepared to spend money on good pairs/sets.