An old friend who works as a mastering engineer (and engineer) for Chesky Records recommended the Monster Turbine Pro earbuds to me twice in the last few years. But the right opportunity to obtain them only came along recently: a birthday present where I kicked in a bit of the cash to make them my sole present.
I LOVE these earbuds, probably just about as much (and for many of the same reasons) as I LOVE my AKG K701 headphones. The tonal balance is totally natural and the presentation is very detailed and revealing without being hyped. Also, the bottom end is actually better on the Turbine Pro's than it is on the K701's (which are just a touch soft below 100 Hz). And the Turbines are designed to block outside noise (very effectively) without making your ears feel plugged.
I've owned an iPhone since the first day they came out (my current model is 3G-S), but I never took iTunes seriously until I got the Turbine Pro's. Now I'm ripping my CDs in (at 16_44.1_Wave) and really getting a lot out of the iPhone/Turbine Pro combination. I also think this playback system is helped by the fact that the Turbine Pro's seem to play significantly louder than the stock earbuds at the same volume setting, so you can turn the iPhone volume down and the phone's electronics don't have to work so hard to play at comfortable levels.
The earbuds come with many differently-shaped rubber earpieces, and I'm sure everyone could find something that gives them a great fit; I actually was happy with the ones that were mounted on the buds right out of the box. Of course, YMMV.
http://www.monstercable.com/productdisplay.asp?pin=5466