HeadPhones: Best soundstage?

The only 'cans' designed specifically with that notion in mind were by STAX, electrostatics, The SR-Sigma I believe... they had the diaphram in front like a rectangular 'box' and the sound came from 'in front' of your ears...I think it would be very difficult to find a used pair but they pop up here every now and then and are usually immediately sold.

FWIW, I'm not particularly a fan of headphone's version of soundstaging - I think it's highly overrated and a bit disorienting in some cases. That said here's a few suggestions to check out:

HD800 probably are the dynamic champs
Stax (just came out with a brand new flagship)
AKG K1000 (only available used)

You might also want to look into Smyth Research

I believe binaural recording techniques have been used to create a different "soundfield" for headphone listening. You might want to investigate recordings as well.