[eclectic]

I usually don't use my amps.  Music: acoustic, chanson, and this week-Macy Grey.

 

[winma]

Audio-Technica ATH-AD900's are good for acoustic and classical. 

 

[brendon]

No amp = Consider high-end Grados RS1/RS2,HF2 etc, Audio-Technica AD900/W1000x, Beyerdynamic DT880/990 low ohm  versions or a used Stax system like the Koss ESP 950 with amp.
 
All for under $400 except the Koss which is maybe $50 - $100 more.
 
All the above should work well without any special amplifier.
 
I haven't heard any of them so I dunno which is good for the type of music you mentioned , but they are the top headphones you can use without an amp.

 

[eclectic]

Thank you both-I was leaning twords the ad900 to begin with (and denon d5000, perhaps) .  Thanks for the back-up.

 

[Uncle Erik]

How about an old receiver for $10-$50 and a Sennheiser HD-650?  You'd get great sound.