Relating to a thread in Sonar Producer and Studio forum, here's a quick example I did with Sonitus Compressor showing a Kick drum compressing a Pad via the sidechain. Seeing this thread I thought I'd link the example here as well. The Pad for the first 25 seconds is untouched, when the Kick comes in you should hear obvious ducking and pumping of the Pad.
 
http://soundcloud.com/stoons-1     "Sidechain"

Another classic example would be Daft Punk - One More Time.