Here you go:
http://www.etymotic.com/
The models you will likely want to consider are the ER-6, $139, and the ER-4P, $330, and the ER-4S, $330. Shop around (say, for example,
http://www.headphone.com) for the best price. (That last URL isn't a bad place to look for other choices, either.)
There is a difference between the ER-4S and ER-4P: the ER-4P has higher sensitivity, the ER-4S has a more accurate frequency response. The ER-4P is often better for portable players, because it doesn't require as much power to achieve the same volume. But the ER-4S will provide a little more accurate freuency response, and if your player can drive them, go for it.
But take note, these are combination earplug/earphone---they are designed to provide quite a bit of isolation from external noise. So, they're not good for situations where you need to hear the ambient noise around you!