I am a big fan of Sean O'Malley and his Cardio Coach guided workouts. They combine really interesting music with seriously tough workout intervals.
He has 8 different cardio workouts (I currently own the first 5 and use them regularly) and one weight training workout, and they are all now just $4.95 each!
If you're into exercise, check them out. You download them off the web site, so you can be working out right away. Sean's voice is encouraging (and not remotely hard on the ears :) and he always seems to know just when I'm flagging and say something to get me moving again.
(I get nothing from this recommendation but the satisfaction of helping a guy who's helped me with a LOT of workouts. :)