I suspsect the OP has already made a decision, but for others that stumble across this thread, I'll add my 2 cents.
I just got a pair of Monster iSport iems and I love them. These have the strongest bass I've ever heard in an iem. The fit is incredible. If you get these, be sure to read the instructions on how to insert them. It's certainly not intuitive (it involved holding the ear thingy down as you insert them), but it is easy once you get the hang of it.
They are very lightweight and the cord doesn't tangle. They have good sound isolation, but if you pause your music you can hear somebody talking. This is good so you can talk to somebody ("hey, can I rotate in?") without have to pull a 'bud out and put it back in.
The bass is strong without being boomy and doesn't overpower the highs and mids. I feel like I'm making absolutely no sacrafices regarding sound quality using these in the gym.
They have a unique design in that the sound nozzle pivots in the 'bud body. This allows the nozzle to find a confortable position in your ear. I'm sorry to say that the pair I received from amazon had a problem with this - one of the earbuds had a stiff nozzle that didn't move freely in the earbud body. Replacements are on the way and I'm sure the problem will be solved. Until I get those, the ones I have are certainly usable.
