I have tried K701s (my first and last open phones), D5000s (which are called closed but might as well be open), and DT770s. I currently have DT150s and HD280s (for portable use.)
If open phones were acceptable in my situation, there would be several I would enjoy trying. Since that is not the case, however, my interest is limited to closed phones even better than DT150s. The only model I know of that might stand a chance of being better is DX-1000.
Stax 2050 system
I will sure buy, sooner or later (first "priority"):
and maybe, later:
Denon D?000 (one among 1000, 2000 and 5000)
Stax Omega (that requires money... so I guess it will be in some 20 years or so)
My situation has changed slightly. As much as I love the sound of my DT150s, I can no longer tolerate their lack of comfort. The guy I sold my DT770s to is willing to make a straight trade, so I am getting those back (comfort is much less important to him because his listening sessions are short whereas I listen for hours.)
I would love even higher-end closed phones. The only ones I know of are DX-1000 or DX-700, W5000, D7000 or D5000, and Edition 8 or Edition 9.
The Denons are out because they do not isolate at all. I am very hesitant about W5000 because Audio Technica phones in general have a reputation for very weak bass (and less isolation than my Beyers.) The Ultrasones I have read about all have very low impedance and high sensitivity (making them a bad choice with my amp), and I have read that they are bright which I don't like. In contrast to the W5000s, the JVCs are never available at a significant discount, making them seem like a rather poor deal.
I guess that if the DX-700s ever drop below $500, I will try them. Meanwhile, The DT770s are awesome in every way and I can be happy with them for as long as necessary.