Here is what I have to offer:
HiFiMan HE-1000 v1 (can also provide the v2 pads, which unlike most I do not like as much as v1)
Audeze Mobius
MrSpeakers Ether Flow C with the latest tuning kit (very importantly) with flat pads and stock angled pads as well as ZMF pads I sometimes like more [!]
MrSpeakers Alpha (Sold to a friend but I can likely borrow it)
MrSpeakers MadDog 3.2, stock pads and I think maybe have the Alpha pads?
Fostex T50rp (stock & unmolested)
(Do you see a theme in the previous four?)
Sennheiser HD650, newer release purchased several years ago.
Massdrop Fostex TH-X00 (1st gen/drop) with numerous pad alternatives, natural and artificial material, and perforated or not, from several different manufacturers some made for them others that just fit and I think work better.
Massdrop AKG K7XX (also the 1st gen/drop)
Final Audio Sonoros VI, same as above in regards to numerous pad upgrades / options. This is an interesting duck in that it's a two-way hp w/a BA tweeter. Of all of mine, I'd love to get this one measured the most.
Meze Classics 99 (also sold to my friend but I'm sure I can borrow it)
Phonon SMB-02
Phonon 4000
(would love to see the above two phonons measured the 2nd most. Tyll's measurement of the SMB-02 had a super huge suck-out in the mid treble w/a big spike in distortion. And I just don't hear that. Would love to see if that is confirmed or disputed, chalked up to a bad sample.)
beyerdynamic T50p Tesla
beyerdynamic Lagoon ANC
Focal Spirit One
Yamaha Pro 500
Marshall Major
Koss PortaPro
SONY MDR-HW700DS 9.1ch Wireless Surround Sound Headphone System purchased from Japan
Now, for some serious OGs...
beyerdynamic DT-800, version from two decades ago. I believe the 250 ohm version.
AKG K340 Needs a pad upgrade and re-rubber banding the headband.
Audio Technica ATH-ESW9
AKG K501
AKG K240 Studio
BANG & OLUFSEN [B&O] Form 1
I missed it if mentioned. Can this rig do IEMS? I do not have anywhere near as many iems as others, but have a few to offer.