Fuck noise cancelling headphones, it's a useless gimmick. Get yourself a decent pair of enclosed headphones and they should do all the noise cancellation you could hope for just by virtue of being well-made.
I have the Sennheiser hd280 pro headphones that est mentioned earlier in the thread, which I use for both recreational listening as well as sound engineering stuff and they're absolutely wonderful. As he said they have a more balanced frequency output, so if you want more bass-oriented phones then you may want to look elsewhere, but if you're like me and prefer to hear a more clear and even sound from your headphones, I can't possibly recommend these enough. Sennheiser in general are pretty tits, really.
It might also be worth checking out AKG headphones as well. I think they may be a little on the pricey side, but they're very good, and fuckin' pretty to boot.
As for hearing loss, these are the numbers for "safe listening time" that I have, the amount of time one can listen, on average, without damaging the ears.
< 85dB= 16 hrs
90dB= 8 hrs
92dB= 6 hrs
95dB= 4 hrs
97 dB= 3 hrs
100dB= 2 hrs
102dB= 1.5hrs
105dB= 1hr
110dB=0.5hrs
> 120dB= DON'T
For reference, conversational speech is roughly 60dB, a chainsaw is about 100dB, and 130-140dB is the human threshold of pain.