Actually, some of these companies are legitimate.
They make enough money off of advertising that they can afford to give away free stuff like this. The Free iPod webpage is the most well known one and I've seen different TV shows and news programs get their free iPods. The only problem is that you have to complete one or more free trial offers (I got a credit card, but thats fine, I didn't have one) but now I have to get 5 other people to complete the offer before I get my iPod.
Like I said, It works, but its a f'n hassle.
~Mike