I can't rave about my Shure 535 IEMs enough. I'm even about to spend the $2-300 to get custom molded fittings for them Near-reference quality sound (a little too warm, though it hasn't been an issue so far), great isolation (about 25db), and they are hard to have randomly pulled out of your ears.
Granted, this is well out of the $100 ballpark, but they're still fantastic.
If you're looking for reference quality sound at under $100, look into the Etymotic in-ear headphones. Ridiculously good, though they are a bit weak on the low end of the spectrum (not enough that you won't feel bass on real punchy songs, but enough that they don't sound like any other headphone on the market).
So I am really tempted to get the SE 535s (because they seem like the next level up from the 215s which also fit me really well). The only thing that is stopping me is that the idea/hope that the Westones would be better. Did you do any sort of comparison between the two?
No, when I purchased my 535's from Headroom, they didn't have any Westone in stock (that I recall, it was several months ago). I tried out similarly priced Sennheiser in-ear headphones (ie80 and ie800) as well as another higher priced JH Audio IEM model (JH13, iirc), but the 535's sounded the best to my ears.
I do see that the Westone's offer 4 drivers to the 535's two drivers, but unfortunately Headroom doesn't have the frequency response graphs for them yet. Otherwise, they seem very similar for features & specs (they both appear to use the same ear tips, which is good for finding the one that fits the best).
Of course, I'm lucky enough to live in Headroom's home town, so that helps these kinds of purchases immensely.
The 535s have three drivers, and Shure now has the SE846 if you're interested in quad drivers. But I'll caution that triple and quad drivers don't necessarily make for better sound.
Granted, this is well out of the $100 ballpark, but they're still fantastic.
If you're looking for reference quality sound at under $100, look into the Etymotic in-ear headphones. Ridiculously good, though they are a bit weak on the low end of the spectrum (not enough that you won't feel bass on real punchy songs, but enough that they don't sound like any other headphone on the market).