Let me start off by saying I didn't see an overall "accessories" or "product reviews" section, so I figured I'd start this thread here and if a moderator or admin thinks there's a better place, please forgive me and go ahead and move it to where it should have been! Now that thats out of the way....
I recently purchased a set of Shure E2c's to use with my pda (which at the time was my mp3 player as well). This was my first purchase of higher quality earphones, and I was quite happy with them overall. My two complaints about them were 1. fit with my motorcycle helmet, and 2. lack of low frequency response. I ride my motorcycle just about every day to and from work, and spend a couple hours on it every weekend when the weather and time permit. The shape of the Shure E2c's is such that a little "bulb" sticks up towards the top/back of the ear. This "bulb" always seemed to interfere with putting on and taking off the helmet--enough that it put pressure on the earphones, making them more uncomfortable than they needed to be (sometimes this added discomfort only lasted a few seconds, sometimes it required eventual removal of the helmet and simply starting over). Also, I felt that the low frequency response wasn't quite as good as it should have been with a set of earphones in this price range.
So, after reading more reviews (many from the motorcycling community), I decided to try a pair of the Etymotic ER6i's. These are a much smaller earphone in general than the Shure's were, and are designed to basically fit all the way into the ear (no large bulb sticking out). I also found that the Etymotic ear flanges seem to fit me better than those that came with the Shure earphones. Bass response is much more to my liking as well. I also feel that the noise isolation of the Etymotics is better, but this is most likely due to the better fitting flanges (in my case). The only negative of the Etymotic ER6i's is the "flimsier" cord--the Shure cord feels nice and strong, and its fairly thick, while that of the Etymotics is much thinner, and feels like it could be ripped quite easily. Overall though, for fit, comfort, and sound quality, I'd have to give the Etymotic ER6i the better rating.
Here's a picture of each:
Shure E2c:
Etymotic ER6i: