Lots of nice headphones and headphone amps listed here.
My favorite is the Stax Lambda Nova Signature ear speakers with Stax SRM T1S driver amp.
The LNS ear speaker has an oblong panel that is tilted inward at the front, to direct the sound wave into the ear. The panel is larger than the round Stax SR-009.
These were made just before Stax went under in 2004, and later repurchased by some of the original Stax engineers.
At the time they were the Top Stax.
The SRM T1S driver is an FET/tube output transformer less amp. It uses the tape output connection from a preamp - RCA or balanced (XLR).
They work best with super low noise NOS RCA clear top tubes (60's and 70's) that are very hard to find. I bought a lifetime supply. The stock tubes were run of the mill NOS tubes, and are not the best.
Per a recent Stax plant tour on Head FI they are still used as a reference in R&D.
Although other headphones may have more bass "punch", the Stax can not be beat for warm, clear high resolution, top to bottom sound IMO.
The sound quality will match or exceed the finest state of art speakers. They have a frequency response of 5 hz to 50 khz.
The detail and natural tonal balance is unbelievable!
Sound field is front of center, ear to ear.
Good tubes are a must, and they are not to be passed over if you can find a pair to listen to.
Used ones can be found on Head Fi, although some have worn out electrostatic panels. I bought mine new from an Audio Advisor closeout.
The foam covering over the inside of the phones deteriorates quickly, but the ear pads can be removed, (and stuck back on), and the foam ripped out as they serve no purpose.
http://www.stereophile.com/headphones/889/