What are the best headphones to wear while running?

You need to be able to hear your surroundings, so sound isolation type phones is not a good idea.

Something open, comfortable, non-isolating. I really wouldn't worry about fidelity. What's your source? A smartphone? Might want to consider blue tooth. Lots of runners seem to prefer the "sport" style cans. Turn them down. You need to hear that car..

http://www.headphone.com/headphones/behind-the-neck.php

Tim

Just bought a pair of Jaybird Model Xs that I listen via Bluetooth

from an iPod nano when I run or workout. Very compact earbud design, you pretty much forget about them in use. No problem hearing enough outside sounds though they can subtly lose seal in your ear and you lose some bass.

The Jaybirds have noticeably better fidelity than the over the ear Sennheiser MMX100 BT they replaced (battery crapped out after a couple years), but being over the ear, they never slip.

I really like BT for exercise -- no cord to be annoyed by and with a BT Nano or similar, it's a very minimal rig.