Etymotic Research's noise-isolating headphones are for the purist, and the hf2's extended jack brings their technology to Apple's iPhone and iPod.
The hf2's tech is otherwise similar to the rest of Etymotic's in-ear models, particularly the hf5 on which it's based. This makes for startlingly clear audio: more than once I'd switch to another set of headphones and immediately miss the hf2's clean, crisp sound. They're great for appreciating musicianship--play some jazz, for example, and each instrument sounds terrific.
These headphones don't really rock, though. Bass is always moderate in strength, even with my iPod set to Bass Booster. Songs with midrange get more definition, but a bit less warmth.
The hf2 ships with two sets of foam in-ear cushions and two triple-flanged rubber ones. Etymotic is known for the flanged earbuds, but I preferred the thick foam, which improved bass response and provided more isolation from the outside world.
Speaking of which, the Etymotics are solid performers at noise isolation. On the bike-commute proving grounds, I was able to hear my music on low volume while quieting, but not completely tuning out, the outside world. In my simulated airplane test--sitting in front of a window air conditioner unit, which rattles at 75 decibels (airplanes are even louder), with the iPod's volume just a hair above mute--I could hear the audio perfectly. They performed less well on the subway, where music was audible but the train rumble was not suppressed.
The set also come with a soft leatherette case that's large enough to fit everything but small enough to toss around. Its cord is the standard four feet and picks up noises a little too readily for use during heavy physical activity.
Etymotic's hf2 phones are remarkable in their clarity and dynamic reproduction. I've learned, however, that great doesn't always mean ideal: they're not going to satisfy hip-hop and rock fans who want more oomph in their audio. If you like your music crisp and pure, though, they're a real treat.
Product Page [Etymotic]