I was looking for a pair of used Philips Fidelio L1, then Tyll recommended me towards some Senn HD600's .. But even the HD600's still require an outboard amp (it seems, based on limited reading)..
I'm looking for full-size (don't like on-ear), open headphones for the office.. Recommendations on what to look for used, scratched, and dented is appreciated (lower cost) as I'm not too concerned with how they look when I'm just sitting in my office working.. But I mainly would rather avoid an amp, unless someone has a good amp recommendation in the ultra-cheap range ($20-30?). I'm already pushing my budgetary limits on some headphones!
Realistically I've been lightly looking for a year now, and I could even stand to wait another year. Price is very important!