Not all pet food is made equally. A lot of it is full of corn, by-products, dyes, unhealthy preservatives, filler grains and all sorts of nasty stuff. A lot of pet food companies are perfectly happy to dump cheap leftovers in. Will it kill your dog? No, it has to be nutritionally complete and safe to even be marketed. Is it healthy? Not by a long shot.
Corn is a low quality ingredient you never want to see in your pet food. Corn and low quality grains are two of the biggest culprits when it comes to food allergies in our pets.
Thankfully, there are some excellent dog foods being made these days that include organic, human grade ingredients rather than trash not fit for human consumption.
Examples of low quality foods to avoid: Anything you can find in a grocery store will be low end, Purina, Iams, Eukanuba, Science Diet, Royal Canin, Pedigree, Kibbles n' Bits, Beneful, Ol'Roy.
Examples of high quality foods to look for: Innova, Wellness, Solid Gold, Canidae All Life Stages, Fromm Four Star, Merrick, GO Natural, Nature's Variety Prairie, Nature's Logic, Artemis Fresh Mix, Timber Wolf Organics.
Although the high quality foods are more expensive, you're getting what you're paying for. Less filler material means more concentrated nutrients... this means you typically need to feed far less of the high quality food than you would of the low quality one. Which also means less poop!
A great option is to go with an entirely grainless diet. Many of the high quality foods now put out grainless formulas. Some good grainless diet's include: Innova EVO, Wellness CORE, Blue Wilderness, Nature's Variety Instinct, Orijen, Fromm Surf & Turf, Now! and Sold Gold Barking At The Moon, Taste of the Wild.
Some of the high end foods can be found in common pet stores. Petsmart carries Blue Buffalo products (such as the excellent grain free diet Blue Wilderness). Petco carries Wellness and Solid Gold. If you can't find a food, most of the high quality food brands have websites with store locators on them.
Remember that foods should be switched gradually, especially when switching to a higher quality one, so as not to upset tummies.
Another option for feeding dogs is to feed raw. This is something that should be thoroughly researched before being attempted:
http://www.barfworld.com/
http://www.rawfed.com/
http://www.rawlearning.com/
http://www.wysong.net/controversies/rawmeat.shtml
More on dog food:
http://www.dogfoodproject.com/index.php?page=main (Learn how to determine the quality of your dog's food.)
http://www.dogfoodanalysis.com/dog_food_reviews/ (Dog food reviews. Anything with five or six stars is a great food.)