hd595, hd598, audio Technica ATH-AD700 or possibly Grado sr80i
I had HD595 before and it was pretty good straight from an EMU sound card. I've tried a higher end version of AD700, don't remember the model, and it was pretty "lifeless" with not enough bass/mid-bass punch. The Grado's are fun, even with sr60i (I currently have SR325i and Denon D5000 and they're great). If you'll go with Denon D2000, consider
modding them.

Also, if you end up going with a headphone that needs amping or a DAC, checkout
this blog.