I have fallen in love with the Superlux HD681 for classical music. A pair of AKG K240 velour pads are typically called for (Sam Ash has them - never in stock, but they order them as soon as you place an order), since the stock Superllux pads are not that comfortable. For the cans and pads, it should run a total of about $60-65. I also have tried the AKG K701/2 (sounded good, very power hungry, a little bass shy, but not very comfortable) and have the Beyerdynamic HD660's at work (designed for classical, but closed-back so a bit closed-in sounding, a bit heavy, and also a bit bass shy). As open cans, the HD681s have a very spacious presentation.
Some don't care for the HD681's brightness (there is a treble peak around 7500 hz), but it is not an issue for me on classical music (which is all I listen to). For orchestral music, the added treble energy is preferable for me to get the upper harmonics and a brighter presentation, especially for music recorded in large symphony halls. However, if you listen to a lot of rock or pop, with a lot of cymbals and other content in that frequency range, the HD681 can be somewhat fatiguing.
The bass on the HD681 is not boomy, but very strong. The HD681B has a bit less bass, and the HD681F even less. However, if you like to feel the tuba, bass, low cello, etc. in your bones, the HD681 is nice, and Superlux advertises that the HD681 is voiced for classical music. As with treble, if you're not listening to rock/pop with a lot of constant bass, this is largely a non-issue.
The HD681 is only 32 ohms: very efficient, but the output impedance on your source/amp should be fairly low (4 ohms max?) in order to keep the bass tight.
Hope this helps.