Avocado: Contains percin, which is harmless to humans but toxic to dogs.
Alcohol: Even small amounts can cause vomiting, diarrhea, central nervous system depression, difficulty breathing, coma, and death.
Onions and Chives: Can destroy a dog's red blood cells, leading to anemia. Symptoms include weakness, vomiting, lowered appetite, and breathlessness.
Caffeine: Can be fatal. Symptoms include restlessness, rapid breathing, heart palpitations, muscle tremors, fits and bleeding.
Grapes/Raisins: Can cause kidney failure.
Dairy Products: Can cause diarrhea and other digestive upset as well as set up food allergies.
Macadamia Nuts: Can be fatal. Symptoms include muscle tremors, weakness or paralysis of the hindquarters, vomiting, elevated body temperature, and rapid heart rate.
Candy, Gum, Toothpaste, etc: These are sweetened with xylitol which can cause an increase in the insulin resulting in a drop in blood sugar and possibly liver failure. Symptoms include vomiting, lethargy, loss of coordination, and seizures.
Chocolate: Contains theobromine which causes vomiting, diarrhea, excessive thirst and potentially death.
Fat Trimmings: Fat trimmings can cause pancreatitis in dogs.
Bones: Can splinter and cause an obstruction or lacerations of your dog's digestive system. Always supervise your dog when he's chewing on a bone.
Persimmons: The seeds of persimmons can cause inflammation of the small intestine.
Peaches, and Plums: The pits contain cyanide.
Raw Eggs: Potentially contain bacteria like Salmonella or E. coli. Also, an enzyme in raw eggs interferes with the absorption of a particular B vitamin. This can cause skin irritation and problems with your dog's coat if the raw eggs are fed for an extended period of time.
Raw Fish: Certain kinds of fish can contain a parasite that causes "fish disease" and if not treated, it can be fatal. Cooking the fish will kill the parasite.
Salt: Eating too much salt can cause excessive thirst and urination and lead to sodium ion poisoning. Symptoms include vomiting, diarrhea, depression, tremors, elevated body temperature, and seizures. It may even cause death.
Your Medicine: Reactions to drugs prescribed for humans is the most common cause of poisoning in dogs. Keep all medicines out of your dog's reach and never give them any unless instructed to do so by a vet.