You should strongly consider the MrSpeakers Mad Dogs for 300. I have the 250 dollar model (smaller earpads) and I feel they outperform many 500-ish dollar headphones I have used before - including the Denon D5000, Grado PS500 and Senn HD600.
they're mostly flat in response. a bit dark in tonality. Their imaging is very good but the soundstage is not as tall or wide as, say, the HD650.
+1 also HD650 are to picky with what gear you pairing them and with all pairings except one i heard thry are lacking sub-bass and that's why are for sale