The Sennheiser 280s are available from musiciansfriend.com for $100. IMHO anything better than these and you'll be listening to the inadequacies of MP3. Even with these $100 headphones you can clearly hear the difference between MP3s and CDs. I wouldn't spend more if I were you ... or get two pairs 280pros for work and used 580/600s for home.
BTW the 280 pros are very efficient ... you will not need an amplifier. A battery powered portable will drive them very loud.
BTW the 280 pros are very efficient ... you will not need an amplifier. A battery powered portable will drive them very loud.