KSC 55's or Senn PMX 100. I don't like the over the head setup, but if you do, the Senn PX 100's are a good choice. I'm currently working on this myself--I'm looking for something for the gym. I've used my UE10's there in the past, but as time goes on, I get more and more leery of using them in the gym. I'll probably stick to using them in non-strenuos situations. I'm also getting to the point where I prefer the sound to the open phones when working out anyway--the UE's are great for relaxed listening, when you have nothing else going on around you and you're concentrating on the music, but the open phones give a different, more visceral though less accurate presentation, which is kind of good for the gym.
The Koss 75's don't work for me either--they just don't clip on well. I've been toying with the idea of getting a sportapro headband, and clipping them into this. The KSC 55's sound fantastic, but they're uncomfortable. Think of it as a spike slowly but persistently grinding into your temple...
I have the PMX 100's (which should sound like the PX 100's, which I've listened to before) on the way. I actually slightly prefer the Senn PX 100 sound (the new PX 100's, that is which are supposedly brighter than the older ones--I've only heard the newer ones, so I don't have anything to compare to) to the KSC's (although for the money, the KSC's are unbelievably good. It's amazing that Koss can make something as good--and cheap--as the 55's on one hand, then come out with something as awful as the plug. It's a plug alright; it just should be used to plug something than your ears). That's going to be blasphemy to some, but they're my ears...
I'm hoping the PMX's will be more comfortable than the KSC 55's--from what I've read, they're better than the Koss 55's from a comfort standpoint, but we'll see. If not, I'll buy a pair of sportapro's and swap drivers with the 75's, but I'm a bit leery of the sportapro neckband longterm. Maybe I'll email Koss and see if I can just get a sportapro neckband; wonder if anyone else has tried this.
I'm turned off by the iGrado's--although I haven't heard them, the reviews have been less than stellar. I have the SR 60's (which I love), and it would be heartbreaking if the iGrado's were significantly different from the 60's in SQ, and apparently they are.