Good stuff, Perseus!
Here are a few more tips that will help you once you start shopping.
Try before you buy
Sounds obvious? It's harder than you think. If you're buying blind online, you have no easy way to try before you buy. Inexpensive earbud headphones usually come heat-sealed in tough plastic that you need a crowbar to open, so even if you can try your new phones, there's no way you can return them if you don't like them. That's why it's best to buy headphones from a hi-fi shop if you possibly can. Quite often they have a few different demonstration pairs you can test out. There's nothing to stop you testing headphones in a shop and buying online later if you can get a better deal that way. An alternative is to ask a few of your friends what they use and listen to their headphones. Aim to try at least three or four different pairs.
Listen to your own music and your own equipment
The sounds you hear are generated by some sort of stereo equipment and then played through the headphones into your ear. Both the equipment itself and the headphones will change the quality of the sound, so if you're trying to compare headphones make sure you use the same stereo equipment in each case—and listen to some very familiar music. If you're trying expensive headphones in a hi-fi shop, take in your own equipment for the test—even a portable CD player or MP3 player is better than nothing. Remember, the quality of MP3 tracks is always poorer than that of the same tracks played from a CD (because MP3 is a highly compressed digital format). In other words, a pair of headphones will sound worse with an iPod or MP3 player than with a CD player, even when they're playing the same track.
Think about how you'll use them and then pick the type that's best suited to your needs
Big or small? The general rule is that bigger sounds better. Bigger speakers are usually more expensive and made to a higher quality than smaller ones. The same is true of headphones and earbuds: big headphones that sit over your ears usually sound better than small earbuds. Of course, there are high-quality, very expensive earbuds just as there are high-quality headphones. If you want some phones for listening mainly on the move, earbuds are generally the best bet.
Open or closed? Open-backed phones have vents in the back of the case (facing away from your ear) to let air move in and out; closed-backed phones are completely sealed. Open-backed phones generally sound better than closed-back ones, because open-backs allow sound to move more freely and with less distortion inside. If you're buying phones for private home listening in a room where other people will be chattering away or listening to the TV, you may prefer a closed-backed pair. Similarly, if you intend to use your phones on a train, bus, or plane, closed-backed headphones will reduce the background noise you hear and the disturbance you cause to other people—although noise-cancelling headphones are generally better for travel use.
Noise-cancelling or not? If you're listening to headphones in a noisy place (on a plane or in a noisy home), background sounds can seriously reduce the quality of the experience. Noise-cancelling phones can be a big help and they come in two main kinds. Passive noise reduction phones (like Etymotic earbuds) have earpieces that make a seal with your ear canal, preventing unwanted sound from getting in. Active noise reduction phones (such as Bose QuietComfort) have a little microphone on the outer case. The microphone samples the background noise and an electronic circuit inside the phones automatically compensates for it.
Here's a quick summary.
There are a lot of choices out there and I could use some help. Does anyone have some good rules of thumb to help me narrow the field down?
Thanks.