On the slightly lower end and a bit more rugged, in my opinion, are the Ultimate Ears Studio 3. They have replaceable cables and provide a better sound isolation experience for me than the ER 6i. Plus they are around $99.
And you can find more info on them at http://www.head-fi.org as well.
ER 6i from Etymotic Research - I can't hear you! No, really, I can't hear you!!