I've posted a number of times that I'm an Sennheiser HD600 guy through and through, but for kicks I'll throw another one out there: check out the Superlux HD668B. Incredibly cheap headphones that sound pretty amazing. I mean, they sound REALLY good!
They aren't as open and "airy" as the HD600, but they are louder and they pair better with a lot of amplifiers. For that price, you can buy one for a back up, and a 2nd pair as its backup.