In order of preference:
K701 - stellar headphone, has a great reputation here, and recently discontinued. Bass and treble aren't as loud as the midrange, which puts off some people. It needs a little dynamat to avoid sounding a little plasticky.
K702 - most people want more bass out of K701 and K702 sounds a little more balanced at that, plus K701 is now discontinued. There's also the often recommended Q701 lately, but I think that it sounds like @ss without removing the foam discs behind the little black grills.
Another vote for HD650 here, especially with chamber music.
Another vote for HD600, haven't tried it in a long time, but when I had it I listened to symphonies and/or piano the most with it. Great tonal balance. HD6x0 tend to sound more "believable" when it comes to vocals, strings, and more.
K601 - A slight downgrade from K702 and such, subbass is AWOL. There's the newer version, K612, but I haven't tried it. Best tonal balance from AKG.
HD558 - HD6x0 on a budget, lol!
ATH-M50x with HD280 earpads or memory foam HM5 earpads - it sounds addictingly "right" and natural. With the original earpads it does not sound good with classical.
HDH50 - best tonal balance out of everything mentioned here and probably anything else that may be mentioned later in this thread, although I don't know jack about the Stax listed or K340. Good for all types of classical, but better suited to small ensembles.
K545 with HD280 earpads or memory foam HM5 earpads
K501 - a downgraded version of K701 with the bass and treble dialed down further, basically. Subbass is also AWOL. Discontinued long ago and has a better headband.
SRH840 - tends to sound more "believable" like the Senns mentioned, but is warmer in sound. It can be a bit harsh in the treble with some recordings.
Grados + organ can be quite fun.