I've learned so much from these boards over the past few weeks since I got a DAP, so I'll try to give a little back.
I had a pair of Sennheiser PX100s that I really liked. But for gym use I wanted something that didn't have pads that would get all sweaty, and that had some isolation capacity to block out the muzak they play. So I bought a pair of the Sony EX71s from amazon.com for about US$32. To me, they suffered immeasurably from comparison with the PX100s. The sound was not up to par for me - big sloppy bass, not much midrange and kind of a screechy treble to my admittedly non-audiophile ears. The cord was highly microphonic - every small touch resulted in a boom in my ears. I had to wrap the cord over my ears and thread it behind my back under my shirt to get an acceptable result. Finally, the cord is very short, with a connection plug to a longer extension. Combine the weight of this connection plug with a much shorter cord to the left ear than the right, and normal gym activity made the left bud constantly work out of my ear. I returned these within a week, and I've ordered a pair of Shure e2's from an e-Bay merchant for about $80 including shipping - hope I like those better.