Iams has a dog food rebate offer out right now and you can print the form from here.
Buy any 2 lbs or larger bag of Iams dog food, and mail it in with the printable form, upc, and dated cash register receipt showing purchase between 2/1/2011 and 6/30/2011. The fine print does state it is limited to the first 15,000 submissions.
I hate it when companies do this. How do you know when you purchase that you aren't number 15,001?
Don't have a dog, but have some kitties instead? The form for the cat food offer can be found here. The terms and conditions are pretty much identical, except for sizing.