A rather interesting contest type thing run by (who else?) Pepsi. When you buy specially-marked bottles of Pepsi products, you can earn 100 points under the cap. (You can also get a free bottle of soda or discounts on shoes.) The "points" are actually ten digit alpha-numerical codes that look like this:
You then go to http://www.pepsistuff.com/ and type this code in. (After you log in, of course.) If the code is valid, (which the above is not) you get 100 points. You can trade these points in for hats, MP3s, MP3 players, and other useless things. But they're free useless things. And free stuff is always cool.