Two excellent IEM earphones are the
Ultimate Ears Super.fi 5 Pro and the
Klipsch Image X10. I know the Klipsch goes a bit over budget.
Both earphones give excellent bass response (once you get the ear tip fit right) and provide good sound isolation.
The Ultimate Ears Super.fi 5 Pro has an excellent over the ear fit system - the cable moulds over your ear and holds the earphone in. However, the earphone is relatively large, compared with the Klipsch.
I would say the Klipsch Image has an even better fit than the Super.fi Pro as it's absolutely miniature, making it much less of a fiddle to get in your ear. The Klipsch Image is a very good earphone for extended listening sessions due to it's comfort.
Sound quality wise they are both excellent. The Klipsch has a particularly well defined bass response - it's not just heavy bass, it's very accurate bass. The mids are a little recessed on the Klipsch, compared with the Super.fi 5 Pro.