HE400 is probably the one of the best performance-price ratio you can get under $400 if you are considering open headphones.
it is seems to me to be extremely balanced close to ultra balanced while having great bass. of course, there are more ultra balanced options, but the price jumps significantly up.
For closed options, I would consider the Sennheiser Momentum (decently neutral; portable), the Sony MDR-1R (extremely comfortable - most comfortable closed,portable headphones I have ever tried), and the AKG K550 (amazingly flat sound w/ crazy soundstage for closed headphones and great bass extension - not really portable)
For open options under $400 besides the HE400 (which would be on the top of my list), Sennheiser HD 600/650 have been really popular for a long time and the AKG K701/702 are solid options. Note: the Sennheiser HD600/650 and the HE500 really benefit from amping (so you might end up throwing $50-100+ down on an amp to get closer to their SQ potential)
Edited by money4me247 - 12/14/13 at 3:29pm