Beyerdynamic DT531.
Why? Well, where can I begin....
1. Its extremely comfortable - this quality should not be underestimated in a headphone IMHO. And these are as good as anything, maybe even better than the Sony MDR-CD3000 because its lighter, and the pads are friendlier to the touch.
2. Extremely forgiving - these headphones will not bite you if you do not have a great amp or source, they will still sound good, unlike many headphones. However, if you feed them a good signal, they sound superb! Not only that, but I have never got the impression they were picky about amplification or sources.
3. Lively sound - These are one of the liveliest sounding headphones I've ever had the pleasure of listening to, but they manage to do it without being fatiguing. Slightly bright balance, but never offensive. Good detail too. Yet they manage to sound extremely coherent at the same time - music sounds like music, it does not sound like an over-seperated collection of sound effects.
4. Superb bass performance - These cans have really good bass. They leave the MDR-CD3000 way behind on my system for slam and punch. The depth they have will not win any awards, but its surely good enough for 99% of people out there, and again, I feel it better than the CD3000. These cans have the best quality bass I've ever heard from any headphones in my possession, at least on my system anyway.
5. Bargain price - These headphones are reasonably priced. They are cheaper than the Sennheiser HD580, Grado SR80, Sony MDR-CD1700 and AKG K240 Studios, yet they sound better than any of those. These headphones will handily compete with headphones costing many times their price IMO. They arent perfect, but they have a REALLY likeable combination of qualities, and I'm surprised they arent more popular round here. Nevertheless, your chance to sample these cans is all but gone, unless you pick up some second hand cans.
I like these headphones so much that I have bought myself another pair, and they will be replacing my MDR-CD3000's