Looking for an off-camera mixer
 

I've been talking to a few friends about audio (in respect to DV, of course), and one suggested that I try working with an off-camera, battery powered mixer. He described something that could be worn on a sling so that it sits at your hip. A boom op would use it to manage the level of the mic (or mics, as the situation may be), riding the gain to ensure that the audio doesn't clip.

My questions are:

1. Where can I get such an animal? (My friend couldn't tell me, he was rather drunk :) )
2. Does anyone have any suggestions about using this method?
3. Is there anything else I should know?

Thanks to all in advance,
Greg Covey