There's an interesting new site offering free gifts called Bid4Prizes. It's based upon a variation of the auction process: instead of the winning bid being the highest, it's actually the lowest bid which wins.
Aha, but there's obviously a catch to this, right? Such a sweepstake would quickly go bust as everone would bid one cent. And indeed there is acatch but it's one that just makes everything more interesting. It's the lowest unique bid that wins the item. Now that does make it interesting as you need to outgame everyone else to make the lowest bid that only one person does in fact make.
It's a fairly impressive list of prizes too: Apple iPhones, HDTV's and also straight cash prizes.
If you know your game theory this should be a really fun site to play around with so click through any of the above links to see how it works.