An excellent Penn and Teller episode, I believe it was titled 'family values'.
There was an MTV True Life episode with polyamory in the title (though it dealt more with open relationships I thought)
Montel had one episode on it which was OK but it over-sexualized the issue in an immature fashion in my opinion.
There is a regular Youtube show that's quite good about polyamory
I have some other resources and already have a thread on polyamory films, if you folks want I could try to bring everything I've found together and make a comprehensive thread sometime.