There is are naturally occurring stimulants theobromine and methylxanthine compounds found in cocoa beans will cause vomiting, heart problems, seizures and death in dogs. Despite it’s morbid premise this amazing National Geographic infographic will tell you exactly how much chocolate it takes to kill your dog. Other foods to keep Fido and Spot away from include:

Alcohol - Alcohol depresses brain function in dogs and can send them into a coma. It can cause further damage by turning their blood acidic.
Onion - An onions damage to canine hemoglobin is cumulative, so small tastes over time can be worse than wolfing down the whole bulb. It will eventually cause anemia.
Grapes - Toxicologists have found that grapes and raisins can cause acute renal and kidney failure. As few as ten raisins or grapes, anywhere from nine ounces (255 grams) to two pounds (0.9 kilograms), could be fatal.
Macadamia Nuts - Experts have yet to determine why just a few of these nuts can produce tremors, even temporary paralysis, in a dog’s hind legs.
Garlic - Dogs don’t have the necessary enzyme to properly breakdown the compound thiosulphate so garlic, in any form, breaks down a dog’s red blood cells, and large amounts over time can lead to anemia and possible kidney failure from leaking hemoglobin.
Coffee - The caffeine in a cup of java is a methylxanthine compound that binds to receptors on cell surfaces, precluding the normal compounds from attaching there.
Bread - Like alcohol, ingestion of yeast can cause fatal damage. Active yeast found in raw bread dough releases alcohol as it grows.