First of all, great thread. I've been looking for relatively neutral headphones at around the $100 price point. Recently I got a chance to try a bunch of studio headphones at a local SamAsh, using my phone as a source (HTC One). Just wanted to put some thoughts down on those considering a couple of popular models.
First studio headphone I ever owned was the MDR-V6. Wow. Never before have I heard a more mid-forward headphone, but the touch of high end sparkle lead to some amazing details I never picked out before. Because I listen to both electronic music and metal, midrange has to be both incredibly neutral so that it doesn't shear my ears apart like the V6 but also not too recessed as to sound unrealistic. The V6 had way too much upper mids for my taste. Sold them.
The next headphone I purchased was interesting, at first they sounded awesome and I thought they were way more neutral and that they were what neutral should sound like since I had little to compare to, that was the HD 280 Pro. Now that I've heard many other cans, I can tell you that these are emphasized in sub-bass, have a slightly woody mid, rolled off highs, and recessed upperm mids. Their sub-bass has awesome extension, but there's a problem. The mid-bass is sucked out by at least 5-8 dB and that along with the other sonic problems the headphone has make them nearly unusable for someone who wants a neutral sound. I actually still have them though, if only for their sub-bass for some electronic music and also for tracking guitar, since I'm a hobbyist guitarist. Insane isolation is by far their strongest suit.
The next I tried was the AKG K240 Studio. Wow, way too colored for being labeled "Studio." Almost nonexistent sub-bass, an exaggerated mid and upper bass, and a glossy 10 kHz peak make these far from neutral. Their mids aren't that bad but still have some grain to them. These are quite fun and have a very decent soundstage for the price, but alas I'm just going to give them to my father who loves to listen to The Beatles. They seem to work awesomely with that kind of music, but not mine.
My current favorite is the Shure SRH440. I tried KNS 6400, M50, SRH840, a Superlux and a Samson at a local SamAsh and the SRH440 won out over all of them in terms of just sounding "right" to my ears. It's too bad they didn't have any HD600s or Beyers to demo. I've always wanted to try those. So that's what I'm using now, they are slightly upper-mid forward but the balance of bass, mids, and treble is fantastic for their price, and they're comfortable to me too while retaining solid build quality. The only real downside is recessed sub-bass.
I'm working with a grad student budget here, so sorry that I can't contribute at all to peoples' notions on HD800s and LCD3s of the world. Hope this helps some people shopping around this price range for relatively neutral studio headphones.