Best headphones you've ever heard/used

The problem with in-ear 'phone for me has always been the positioning or soundstaging. Even good in ears like the etymotics sound 'wrong' not because any part of the frequency range is off, but because the imaging is wrong. All headphones sound like the soundstage is inside your head to varying degrees, but larger open headphones are not as bad at this as any other kind. In ears dont even bounce the sound off your outer ear the pinnae (sorry if I spelt that wrong) and all the other ridges etc on your ear. Believe it or not this is an important part of sound shaping and decoding.
To me, the etymotics and I'm totally guessing here, the shures would have a similar problem. They get fatuiging fast because they your brain knows that the imaging is wrong. I can very well believe that not everyone has the same reaction to headphones and in-ears (and I'm still a headphone fan despite all I say) but that's my reaction to headphones.
Of course there are problems with open phones. Other pointed out the problems when using them outdoors. I listen to mine at night in the bedroom when I dont want to disturb, but I can still listen at reasonable levels. For other uses, other phones may be a better match.
Just my $0.02.

Rsbeck, how is the tonal balance of the Shure e3's compared to the hd-580s? do the Shure's have good bass, or do they sound thin?

Bass *response* seems remarkably similar in the E3's and HD580's, but the bass seems more *detailed* and specific in the Shure E3's. What distinguishes the E3's from the HD580's are the dynamics. The 580's seem to smooth out the dynamic level of all of the instruments while the E3's are more specific, have more punch, air, and variety. Also, I have not heard the Etymotics, but I can say that the Shure E3's do cause the singer and other instruments to image in your head. I used to love my Sennheiser HD580's -- but the more I go back and forth between them and the Shure E3's, the more I find myself eager to get back to the E3's. They are accurate *and* musical. I find myself reaching for the most overused cliche' in audo -- damn if the music doesn't just come alive with the E3's. And I do not find them fatiguing,
which is surprising considering the level of detail, dynamic complexity, and the fact that they are *in* my ears. I fell asleep with them in my ears last night, which tells you something. Whether or not these have enough bass prominance will be a matter of taste, but I feel confident in saying the "level" of bass is quite similar to the Sennheiser HD580's. The E3's do a far better job of communicating rythmic drive, which accounts for the constant "head bobbing" and foot tapping while wearing the E3's.

I'm kind of repeating these comments from another thread, so please excuse me if you read this before.
I sold my Senn 600s (they were claustrophobic & had a distant sound & miniaturized instruments too much for me). I replaced them with Grado RS1's that I really love: relaxing, not edgy, they don't shout either. It is an upfront sound, though, but not assaultive at all. I have found myself listening for hours, way longer than planned. I use a Headroom Max amp. One warning: you must buy the Comfy pads (available from Headroom I believe) to replace the stock pads. With the comfy pads, the Grados are extremely comfortable, resting lightly on the ear, not around it; no sweat. I really swear by the RS1s. Get a nice mellow cable & a relaxing CD player (I have an Accuphase DP75V) & you won't miss having a speakerbased system.

The Etymotic Logic ER-4S's are by far the best I've heard. I prefer them to the Sennheiser HD-600's and 650's (w/Cardas cable upgrade). Detailed, extended and neutral, with a nice, intimate "head space." The foam ear pads work best for me.

The Sennheiser MX-500 earbuds, at $20, are the best cheap headphones I've used.