I just purchased the Shure E310s from Headphone.com for use nearly exclusively at the gym and on planes, etc.
We'll see how they sound, but everyone on this website seems to like them. They offer good bass along with good mids.
I had originally purchased the Denon 751Ks but I had them for three days and the right driver went out completely. So I decided that Denon should stick to AV receivers and forget about getting into the headphone market.
I'm looking forward to...