I use Ultimate Ears Triple-Fi 10, which have apparently been replaced with the UE 900[1]. They have great isolation with Comply Foam and surprising quality for IEMs. The replaceable cord is also a great feature, so when it inevitably gets a kink that kills stereo, you can replace it without spending $$$ on a new pair. The only problem I've had is that one of them has gotten loose where the cord connects so it sometimes falls off, but usually they're good through the day. This may have been fixed in the newer version.

1. http://ue.logitech.com/en-us/product/ue900