Here's an offer running for the next week at Shaws. It might show up in other related stores (some Albertsons, Acme, Jewel, Shop N Save, and others) at some point.
"Purchase 4 participating General Mills products between 7/03 and 7/09 and get a free Redbox one night rental."
Specific products are listed, not all GM products and sizes are eligible, check the circular or shelf displays. They include Betty Crocker Fruit products, Sunkist Fruit snacks, various GM cereals, and Yoplait Trix yogurt.
In general these types of offers are nice to know about if you already are buying one or more of eligible products, maybe you can stock up on them and get a free movie. But in my opinion you should resist being tempted to stock up on things such as the eligible 9oz size cereals, when buying the larger 28oz box would save you more than the value of the Redbox code. Be smart.