HeyItsFree.net is a good, reliable site for freebie offers, one that I check regularly, and they also have some good information on the business of freebie-ing, like this new article on how the author investigates and dismisses scammy freebie offers.
If you're a savvy Internet user, you can probably spot a scam pretty quickly, too - even if you don't know what you're looking for in so many words, you can tell if something "feels" wrong or not legit. But this article has some useful, concrete tips for verifying the ownership of a site and identifying shifty, skeezy business tactics that should make you suspicious about giving away your personal information.
Be cautious, be safe out there! The Internet is a dangerous place, and it's not known for free Snuggies.