i'm in the same situation and while i can offer no opinion on headphones, i can tell you what i've been looking at.
I've been looking hard at all kinds of headphones for rap/hip hop style music and i think i'm close by saying i'm interested in the ultrasone HFI series. Right now, I'm doing research on which ones would be the best: HFI-580 or 680 (which are both around the $170-190 range on amazon) or ponying up for the HFI-780's (which are about $250 on their as well).
i was actually reading an old thread where wind016 said he has purchased a pair and can probably shed more light on them for you OP
edit: also just came across the ultrasone pro-750, so not sure how that compares either.
Edited by JVinci - 12/30/10 at 10:46pm