the best possible earphones you can get are the
Shure SCL2 (formerly the e2c).
(at least within a reasonable price range).
this is coming from my crazy sound engineer and audiophile friends.
I managed to find a pair for $50 shipped.
They really do sound amazing, and they are in ear, so they basically act as ear plugs so they isolate the sound. they come with an assortment of rubber and foam tips that go in your ears so you get a perfect fit and seal.
they sound AMAZING, full rich, and the bass is very crisp and clear. I've never experienced any earphones with sound like this.
if you do get them, just make sure you put on the right tips, because a bad seal will make them sound like $5 earphones. read the
amazon reviews if you are curious.
almost all the people giving it bad reviews did not fit them correctly in their ears or are audiophiles used to buying $300-$400 earphones.
oh, and one last thing with in-ear earphones....
be careful... don't walk around in a busy city with these things in your ears, you can't hear cars, bicycles, or anything that my hit you or even kill you. if you want to do this, it's best to get some cheap earbuds for that (but still be careful of volume).
that brings me to another point: volume. the closer a sound source is, the more intense it is. these things go INTO your ear, so they are VERY close to your ear. i have my volume set on about half what i used to. start very low, and slowly increase it. it's possible to accidentally go too high which is dangerous. with non-isolating earphones, i usually just turned the volume up so i couldn't hear anything besides the music. but with these, you can never hear anything besides the music... so really you don't need to have them very loud.