My opinion..... Grado SR80 with modified Sennheiser 414 pads, Allessandro MS1, Fostex T50RP,Fostex T20RP,KOSS UR40,Sennheiser HD497 if you can find them, maybe KOSS KTX Pro-1, KSC 35,KSC50,KSC55,KSC75,Portapro,Sportapro....probabl y in the same sound league actually according to taste...but cheaper.
Of course everyones tastes and opinions vary,and im sure there are more to choose from out there.
I like the sony MDR-v6s. Cups around your ears while remaining relatively inconspicuous, can be driven by most all electronic devices, built like a tank, and when teamed up with beyer 250 pads they become one of the most comfy headphones out there.
As far as sound goes its definitely an upgrade overall but most notably in the bass department. There are some better sounding headphones out there, aka SR60s, but nothing beats the v6s functionality.
Some other suggestions include:
-Sennheiser HD280 pro- mellow with less emphasis on bass
-Alessandro MS-1- awesome all around sound, no soundstage for that 3-D sound tho
if your into earplug headphones
-Panasonic HJE70- for good bass without sacraficing mids-highs
-Etymotic ER-6i- for clarity and detail but is basslite
-Audio Technica CK7- dont know much about these, seems good