i had a pair of portapros... got them at the sale when koss had them at half off. i didnt think they were impressive until i listened to my other friends' headphones....wow, TOTALLY blew them away. theyre still going for 35$ at amazon with free shipping, btw. as good as they sound, theyre quite ugly. theyre not unbearable by any means, but not the most attractive headphones. theyre alot smaller than they look in pictures, so its not that bad. i just didnt like them because i dont like headphones--the bands get in the way of my ear.
i sold them for a pair of Koss KSC-35
these use the same drivers as the KSC-50, but its almost unanimously agreed that these sound way better...and, most of the time, better than the Porta Pros. theyre earclips ..essentially the exact same ones from the portapros but just with clips for your ear..theyre supposed to fit alot better than the ksc-50s, too. you can get them for 29.99$ from koss.com
as far as all the other headphones mentioned here...they sound worse. the grado sr-80 are good, and i really want a pair, but theyre larger, more expensive, and not as portable.
lastly, if you want earphones, get sennheiser mx500... theyre 15$ shipped from newegg