I second the HD600/HD650 recommendation. I just got a pair of HD600s over the weekend and absolutely love them. They're extremely spacious, great imaging, incredible detail, and really nice sound signature. I hear that the HD650s are also very nice, but very slightly more dark/bass prominent. For hip-hop/electronic and heavier rock, the HD650s might be preferrable but I actually haven't heard them. My HD600s are certainly adequate for hip-hop and electronica, but they're not ideal. I bought mine to compliment my closed planar magnetic Mad Dog Pros, which do have a fantastic sound signature for hip-hop; really liquid sound, bass-oriented and dark but not overwhelmingly so, yet still detailed. To be honest, after receiving the HD600s I might like them better than the MDPs. Just a technically better headphone, more detail and a better soundstage, but I still have to do more work for a detailed comparison.
To be honest I hear bad things about the HD700s. They apparently have a sibilance to them I know I'd find offensive. Your mileage might vary, though.