When I’m doing cardio, I listen to the radio and flip stations quite a bit. When I’m lifting weights, I don’t like to listen to anything.
Pumpin’ doof, it’s the only music that can drag me off the sofa 
Whatever the gym’s playing whilst watching closed caption CNN.
John Phillip Sousa
*I wanted to buy some other marching tapes online, and holy shit, all kinds of Nazi sites came up!
running/cardio - Goa Trance
Lifting - Angry rock type music (Korn, Limp Bizkit, Godsmack)
Sort of like Eve said – people screaming. With energy, not agony.
When I run in the park…sounds of the park.
When I do yoga…Enya 
“What do you listen to when you exorcize?”
I prefer a classical theme or one of those uplifting conservative hymns like “get thee behind me, foul fiend” or “the Lord shall smite the unworthy with his mighty hammer” or something like that.
Oh … you mean “exercise”! Oops!
I don’t really exercise … I walk my dog for 2-3 hours a day, so I mostly listen to her barking or people screaming for mercy from treetops
Currently on my MP3 player as I hit the treadmill:
Zwan
Eminem
Tea Party
Coldplay
Incubus
Finger Eleven
The Police
Gob
This is my 1000th post. I thought I’d use it here.
I listen to Assemblage 23, VNV Nation, Apoptygma Berzerk, and other assorted ebm/goth music, unless I’m doing dance practice, in which case I listen to classic Arabic music like Oum Kathoulm, or Arabic pop musicians like Tarkan or Amr Diab.
Creaking Joints
I’ve found that the only music I can listen to while on the treadmill is completely different from anything I’d ordinarily prefer to listen to. Consequently, I find myself walking/jogging to the tunes of such artists as The Bangles, Madonna and, yes, Cher. Unfortunately for my dogs (show tune aficionados for the most part), Cher’s Believe CD is the perfect tempo for treading.
For cardio, I need something that pushes me. So I go for fast power pop/punk.
The Dickies are great for cardio.
When I’m in a TKD class: Usually something along the lines of other people yelling and getting kicked around.
On my own workouts (bag in the basement, stretching, running): mix CDs, usually techno or hard rock. All-time fave, though, is the soundrack to The Matrix. Only major requirement is a strong beat and LOUD.