Normally for weight training, it is an ever evolving mix of rock including As I lay dying, Heaven shall burn, Taking back sunday, Thursday, etc..
As an alternative, just a few months ago I dove into the realm of the iPod Podcast, which are free to the best of my knowledge. The con for the Podcast is the inability to skip tracks unless of course, fast forwarding. I've done a little research into the file format which is mp4, it appears that you only need an mp3 player which is compatible with this format, I have an iPod shuffle so I can not disprove this theory.
However, if you search the DnB podcasts, you will find a multitude of files. A valuable piece of information about DnB is that it is produced at 180 bpm, which is your optimal stride count per minute for endurance running. My sport is endurance running, which is a different monster than the cardio for fitness athletes, but if you are worth your salt in the fitness business you will be hitting about an hour of cardio and you will be in the runners high zone, not concentrating on anything but just feeling the beat.
A few I have found to like the most are by: DJ Scribbler, Liquidsoundz, Drum & Bass Arena, The Drum N Bass Podcast, and Kongkast. An excellent non-DnB but techno podcast is Radio 538: Tiesto's club life.