I've been playing with headphones lately and I thought you guys might be interested in a couple of real great deals for little $.
First is the Panasonic RP-HTF600
http://www.audiocircle.com/index.php?topic=106654.msg1092474#newFor a little more money is the Fostex T50RP
http://www.audiocircle.com/index.php?topic=105863.0Both of these are easily modded so you can get it to sound near perfect with your equipment and taste. The HTF600 is $30 at Amazon. It's pretty efficient and I think you could get good results with an ipod. I don't use one so I really can't say for sure. The T50RP is $74 at B & H in NY. This has an orthodynamic driver - planer, like a Maggie loudspeaker or some $1000 and up headphones. These aren't as efficient and you really need an amp or a receiver with a little power to drive them properly. IMO the Fostex need modding to get both freq extremes to sound right. But once done, you'll be rewarded with a beautiful sounding pr of phones.