Mountain Dew Game Fuel, WoW-themed flavors of the popular beverage in red and blue (for the Horde and Alliance, respectively), is out in the wild, and at least one of our writers is already a big fan. To show how much they love you (or rather, to try to get you to buy their soda), Mountain Dew will give you a free in-game Battle Bot pet, just for clicking a button on their web site! The button is towards the lower-right, and it'll redirect you to log in to your Battle.net account. Don't worry, it's safe - you can tell by the Battle.net URL. He's a cute little guy. You can see a few screenshots I took in the gallery below.
Apparently you get in-game fuel for your pet, again in red or blue, and when you fuel them up, they will fight opposite colors. If you give your pet blue fuel and the guy next to you gives it red, expect some robot-on-robot fighting action. I'm not sure if you have to get the appropriate fuel for your faction, since it seems you can only get one in-game item per day, and I already got my battle bot. I'll try it tomorrow and see how it goes.
Edit: It looks like we've killed the Mountain Dew website. Keep trying though, it's bound to come back up sometime...
Edit 2: The pet is mailed to all of your characters, so you don't have to decide which one gets it.