Hi. I am looking for a set of headphones that are:

-Closed/open doesn't matter for me.
-inexpensive (the cheaper, the better)
-lightweight
-still comfortable when only listening in one ear (so I guess monitors)
-single entry cord
-long cord if possible

i can suggest the sony MDR-V500DJ.
It's a nice headphone almost the same specs as the famous MDR-V700DJ wich is often used by professional dj's.
It costs about $80, wich is not very cheap but a very good price for the quality u get!

I recommend the
Koss PortaPRO,
-very lightweight
-two chords
- a bit expensive for a portable
-very comfortable because of a special technique
-astounding bass and transparency

looks expensive at first sight but
friends immediately ask me:
'Where can I get one?'
When I let them listen.

How about the Grado SR60? I've got these and they sound awesome with all my portable MP3 players. I also use them with my PC. The cord is really long, and they're pretty comfortable, although they do start to pinch after about 2 hours of listening. You can find them at Headroom for about $69.00.