If you don't mind earphones that sit deep in your ear canals, reviews say the Etymotic ER-6i is an excellent choice. Though they don't deliver as much sonic detail as more expensive options costing several hundred dollars, they still make nuances in your music stand out. Passive sound isolation gives you a peaceful listening experience. As with most in-canal earphones, fit is crucial for best bass response, but they can't deliver the boom of higher-priced headphones even under the best circumstances. Many owners report comfort and durability problems, though others are happy with them. Availability is an issue, but you can buy them directly from the manufacturer. The Klipsch Image S4 (*Est. $70) is also worth considering; it gets excellent reviews and sells for less. An iPhone/iPod/iPad-compatible model of those earphones -- the Klipsch Image S4i (*Est. $100) -- is also available.
CNET and iLounge.com compare the Etymotic ER-6i to other headphones and give useful information on performance and comfort. PC World Good Gear Guide (Australia) also supplies a detailed review. Though less extensive, PCMag.com's review confirms the conclusions of other reviewers. User reviews at Amazon.com are definitely worth a read, with more than 950 owners giving their views on issues such as comfort and durability.
Steve Guttenberg describes the Etymotic ER-6i sound as "extraordinarily fine." Compared to the full-size Grado SR60 headphones, the ER-6i sounds cleaner, though bass response is more impressive on the Grado. However, thin wires on the ER-6i tangle easily, and the earphones can be uncomfortable for some.
Review: Etymotic ER-6i Isolator (White), Steve Guttenberg, Feb. 8, 2005
Jeremy Horwitz, editor of this iPod and iPhone accessory review site, is impressed with the detail on the Etymotic ER-6i, though he says it's not quite as "mind-altering" as the more expensive ER-4P. Noise isolation is also excellent, and the ER-6i earphones are lightweight.
Review: Etymotic Research ER-6i Isolator Earphones, Jeremy Horwitz, Nov. 19, 2004
Australian review site Good Gear Guide, now part of PC World (Australia), lauds the Etymotic ER-6i for its middle and high ranges. Though bass response is weaker, equalizer adjustments help. Overall, the ER-6i earphones are comfortable, though Ross Catanzariti noticed ear soreness after a while. He's also disappointed with the thin cord.
Review: ER6i, Ross Catanzariti, Nov. 24, 2005
In this short review, Bill Machrone says the Etymotic ER-6i have "brilliant clarity," though he found bass response disappointing without equalizer enhancement. Passive noise cancellation is superb, and he rates comfort as very good.
Review: Etymotic ER6i, Bill Machrone, June 22, 2005
Though the site no long sells these earphones, you can still read more than 950 reviews of the Etymotic ER-6i at Amazon.com. Users are impressed with the Etymotic ER-6i's sound quality and passive noise cancellation. Some find them uncomfortable after a while because of the in-ear design. The thin cord has caused issues for quite a few users, though plenty have been happy customers for years.
Review: Etymotic Research ER6i Isolator In-Ear Earphones (White), Contributors to Amazon.com