The ones I like best with the iPod are the audio-technica ath-a100Ti, the blue ones available through audiocubes.com. I mainly use the iPod when I fly or travel and these are good, comfortable, isolated and unlike Etymotics are easy to remove when people come and bug you. Headphones are like a big sign that says "come bug me, I am dying to remove and replace these headphones". Etys are better but the overall experience is better.
Incidentally the new iPod (saw it at Macworld NY) is almost impossible to tell apart from the old iPod. The solid-state scroll wheel looks exactly like the old one and it is very difficult to detect any difference in feel. I had to look really hard at it to make sure I was using a new iPod and not the one I am used to.
I have an iPod, and I love the Koss KSP-35 with it. Very portable, very good-sounding. A match made in heaven!
The KSP-35 sounds quite similar to the SportaPro or PortaPro phones -- they all use the same drivers. Most people on this forum think that of the three, the KSP-35 sounds the best. It is also probably the most comfortable.
I looked around for an even better-sounding pair of headphones. I bought the Sennheiser HD-497, and I found that they sounded almost identical to the KSP-35, but they hurt my ears. Then I went to the headphone.com exhibition in San Francisco, where I tried on about 15 pairs of audiophile 'phones. To my ears, the winner was the Sennheiser HD-580, which sounded a little bit better than the Koss KSC-35, but they cost >$200 and they are not exactly intended for portable use. So, I have decided to abandon my search. I'm thrilled with the KSP-35.
There are no separate bass or treble settings on the iPod. Instead, you can choose from 21 different equalizer settings. Unfortunately, you can't create a custom setting. Nevertheless, they are somewhat helpful. For example, to give my KSC-35s a little bit more midrange, I choose the "Lounge" or "Pop" settings.