I have the shure E5c. They are amazing. Their big selling point is that Dave Matthews Band uses the same technology as the earphones do in their speakers at concerts. Regardless of how impressive that may or may not be, the headphones provide the clearest sound possible (particularly great for listening to jazz) and you wouldn't be able to hear somebody screaming fire in the cubicle next to you if you were wearing them.
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P.S. If you don't feel like shelling this much $$$, I've tried the E3c before and they're also sweet.
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