I just acquired a pair of Sennheiser HD428 headphones for $32usd shipped. They're refurbs, and I've already started to mod them (the vent membrane for lower frequency response)... just need a re-cable now. I picked these are for office use.
I think I'm going to pick up the replacement ear and headband pads from the HD439, I've got pretty oily skin, and will kill the leatherette pads pretty quick.