One good and bad thing about conflicting opinions
Chances are that the differences are so slight that it all boils down to a personal preference. Odds are that you will be more than pleased with either one.
the sr80's and iPod are a good match..
No issues with the ipod (a 2nd gen) being able to drive them. My only gripe is with the sr80's design. The same can be said of the 60's. Thick, inflexible cabling that you can never quite forget about and that seems always in the way or catching on something. They're somewhat uncomfortable on the head too. I rarely use them anymore only because of the horrible ergonomics. It's ashame because I don't know of a better sounding headphone for the money than the 80's. If you don't have a problem with the ergonomics, you'll find the iPod and 60's or 80's a good match.
Good experiences here with iPod & SR-60
I set my girlfriend up with this combo. She really likes it, it sounds good. Only issue with the Grados is thy're not real portable. So she looks kinda silly using them at the gym.
-Eric
No experience with Koss or the Sennheisers..
Personally I think if you're going to go portable, go portable. A good pair of ear buds and an iPod (or Rio Karma, iRiver H series...) is good enough for me. Once you start going with full size head phones, a head phone amp, power supply and accessories, it can get out of control.