In my last 10km race noticed that many of the other runnings race with Ipods. One woman had actually duct taped her bud head phones onto her ears which made me laugh and wish I had a camera. :)
Personally I tend to race unplugged both because I listen to my breathing as a good gauge on pace and its too easy to get distracted listening to music when you should be overtaking and not bumping into people.
Going for a training run is a bit different and listening to music relaxing and a good distraction.
I find the ipod shuffle quite good for running although the headphones aren't the most secure (guess thats why the duct tape is useful)
In terms of mixes I normally just go with PodRunner which is a weekly podcast "Workout music for runners, cyclists, spinners, walkers, or anyone who needs fixed-tempo exercise mixes". Obviously as a podcast the mix is fresh each week and there is some catchy stuff.
Sometimes I'll also pick some eclectic stuff out of my library : U2, Beastie Boys, Rammstein, Armin van Buuren, Paul van Dyk. Anything Trance is great too for a run at a steady pace.
1 day ago