Well, as title suggest, I'm looking for the holy (affordable) grail of headphones.
Current cans are HD280 pro, yes, you can laugh at me, these are my first "real" headphones, I've had them over 2 years now.
Now please don't suggest something like the Senns HD800, because I'm still just a student, and I'm not in the position to sell my car for some (almost perfect) cans.
The top I can spend at the moment is around 200 USD, tough if there's a really good candidate, I might try to save money for it (300 USD is still comfy).
Also, it's a HUGE plus if the headphone is available in popular stores in the US (best buy, target, etc.), the reason for this is that I don't actually live in the US, but I sometimes do some shopping there.
I would also really appreciate if you'd provide frequency charts, as I kinda personally prefer something objectively measured (not trying to bash personal opinion though).
I've come across some really good candidates, well, at least in the flat response aspect, soundstage still needs review-research:
Audio Technica ATH-A900X
Audio Technica ATH-A700X
Audio Technica ATH-A900
Audio Technica ATH-A700
AKG K271 MK II
Shure SRH440
Shure SRH840 (graph from headphone.org shows a crapload of low-bass)
Shure SRH940
Sennheiser HD380 pro
Beyerdynamic DT770 (mids are garbage though)
Edit:
KRK systems KNS 8400 ; bad soundstage according to some reviews.
KRK systems KNS 6400 ; same problem as above, sub par soundstage.
Fischer Audio FA-003 ; praised for neutrality and soundstage, however I can't seem to find them at any store.
BRAINWAVZ HM5 ; rebranded FA-003s, praised as well, also SUPER cheap.