HeadPhones: Best soundstage?

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.

With headphones sound is inside of your head and not in front of you as it is with speakers. It is because when you listen to speakers each ear receives also delayed sound from another speaker (right ear from left speaker). Same can be done in headphones three ways:
- By leaking sound from one cup to another
(special headphone design)
- by hardware cross-feeding with delay
- by software (DSP) manipulation

Often sound cards offer in menu separate choice of headphones that uses DSP cross-feeding and you can compare by switching modes.

Often the rather dramatic effects that might wow someone on speakers, can be downright disorienting and tiresome on headphones. I'm speaking of really dramatic spacial cues (Sgt. Pepper in Stereo comes to mind, to name something mainstream). In these cases a good crossfeed circuit, like Kijanki suggests, can make those recordings much more listenable, and even enjoyable. Otherwise I haven't found that much use for crossfeed myself. I never thought of it as a way of implementing a more realistic soundstage though, and have no experience with the DSP manipulation like the Smyth system uses. Binaural recordings are kind of a novelty and there is precious little actual music recorded in Binaural. It is a pretty amazing effect on headphones though. There seems to be more meditative material that's available in binaural. I can think of only three or four musical recordings though. Finally, the new Stax flagship that is not out yet (AFAIK) is the C32. Here's a thread with some listening impressions of a prototype