[JimmyFrost]

Let me preface this with that I am a padawan audiophile and this is my first post after lurking for months here. None the less I have listened to many headphones in that price range because I am just now ramping up.
 
I know you would like to avoid an amp, but I would consider getting an extremely affordable amp called the HeadAmp4 and some (used - like new) Sennheiser HD 595 or HD 598's. You can get both amp and cans for right around $200.
 
http://www.amazon.com/gp/offer-listing/B0001FTVE0/ref=dp_olp_used?ie=UTF8&condition=used

http://www.amazon.com/ART-HeadAmp4-Channel-Headphone-Amplifier/dp/B000M0TN6U/ref=sr_1_1?s=electronics&ie=UTF8&qid=1315605396&sr=1-1
 
I recently purchased the HD 650's despite my best efforts to stray from Sennheiser  to avoid being a fanboy, but after research and listening to them vs other similar priced headphones, I just like them. 
 
I think the Grado SR125i's are also excellent, but the on ear is so uncomfortable to me. If this is something that doesn't bother you, I'd definitely consider those as well. 
 
Either way I would get an amp for when you are at home. 
 

 

[NoahZ]

Thanks for the suggestion, I really do appreciate it. However I intend to use the headphones outside of my home at least part of the time, and I know that the Senns can't be run unamped. Moreover, my price range was kind of brought down to $150 or less. 
 
For what it's worth, I'm going with my number 1 no-amp-needed choice: Ultrasone PRO 550.