A very comprehensive list which brought me a surprise or two especially about tomatoes!!
What to avoid Reasons to avoid
Alcoholic beverages Can cause intoxication, coma, and death.
Avocado
(fruit, pit, & plant) Can cause difficulty breathing; fluid accumulation in the chest, abdomen and heart; or pancreatitis.
Baby food Can contain onion powder, which can be toxic to dogs. (Please see onion below.) Can also result in nutritional deficiencies, if fed in large amounts.
Bones from fish, poultry, or other meat sources Can cause obstruction or laceration of the digestive system.
Bones
(cooked) Can splinter and tear a dog’s internal organs.
Caffeine
(from coffee, coffee grounds, tea, or tea bags) Stimulates the central nervous and cardiac systems, and can cause vomiting, restlessness, heart palpitations, and even death within hours.
Cat food Generally too high in protein and fats.
Chocolate, coffee, tea, & other caffeine Contain caffeine, theobromine, or theophylline, which can be toxic and affect the heart and nervous systems. Chocolate can cause seizures, coma and death. Baker’s chocolate is the most dangerous. The darker the chocolate, the more dangerous it is. But any chocolate, in large enough amounts, can kill a dog. An ounce of chocolate can poison a 30-pound dog, and many dogs will happily consume more than this. The symptoms may not show up for several hours with death following within twenty-four hours.
Citrus oil extracts Can cause vomiting.
Dairy products Can cause pancreatitis, gas and diarrhoea. A small amount of non-fat, plain yoghurt is usually safe.
Egg whites
(raw) Raw egg whites contain a protein called avidin, which can deplete your dog of biotin, one of the B vitamins. Biotin is essential to your dog’s growth and coat health. The lack of it can cause hair loss, weakness, growth retardation, or skeleton deformity.
Fat trimmings Too much fat or fried foods can cause pancreatitis.
Fruit pips, seeds Apple seeds, cherry pits, and peach pits, pear pips, plums pits, peaches, and apricot pits contain cyanide, which is poisonous.
Grains
(large amounts) Grains should not be given in large amounts or make up a large part of a dog’s diet, but rice is generally safe in small amounts.
Grapes & raisins Can cause kidney failure in dogs. As little as a single serving of raisins can kill him. If the dog doesn't eat enough at one time to be fatal, he can be severely damaged by eating just a few grapes or raisins regularly.
Ham & bacon Contain too much fat and too much salt, and can cause pancreatitis. Also, large breeds of dogs that eat salty food may drink too much water and develop a life-threatening condition called bloat. This is where the stomach fills up with gas and within several hours may twist, causing death.
Hops Unknown compound causes panting, increased heart rate, elevated temperature, seizures, and death.
Human vitamin supplements containing iron Can damage the lining of the digestive system and be toxic to the other organs including the liver and kidneys.
Liver
(large amounts) Raw liver or too much cooked liver (three servings a week) can lead to vitamin A toxicity. This can affect muscles and cause deformed bones, excessive bone growth on the elbows and spine, weight loss, and anorexia.
Macadamia nuts Contain an unknown toxin, which can affect the digestive and nervous systems and muscle. Can cause weakness, muscle tremor and paralysis. These symptoms are usually temporary.
Marijuana Can depress the nervous system, cause vomiting, and changes in the heart rate.
Milk & other dairy products Some adult dogs and cats do not have sufficient amounts of the enzyme lactase, which breaks down the lactose in milk. This can result in diarrhoea. Lactose-free milk products are available for pets.
Mouldy or spoiled food, garbage Can contain multiple toxins causing vomiting and diarrhoea and can also affect other organs.
Mushrooms Can contain toxins, which may affect multiple systems in the body, cause shock, and result in death. Wild mushrooms can cause abdominal pain, drooling, liver damage, kidney damage, vomiting, diarrhoea, convulsions, coma, or death.
Nutmeg Can cause tremors, seizures and death.
Onions & garlic (raw, cooked, or powder) Contain sulfoxides and disulfides, which can damage red blood cells and cause anaemia. Cats are more susceptible than dogs. Garlic is less toxic than onions.
Pennies
(made from the 1980s to today) Contain zinc, which can cause kidney failure and damage to red blood cells. A dog that consumes even one penny can become quite sick, or even die, if the penny is not removed.
Persimmons Seeds can cause intestinal obstruction and enteritis.
Pits from peaches and plums Can cause obstruction of the digestive tract.
Potato, rhubarb, & tomato leaves; potato & tomato stems Contain oxalates, which can affect the digestive, nervous, and urinary systems. This is more of a problem in livestock. Potato peels and green potatoes are dangerous.
Raw eggs Contain an enzyme called avidin, which decreases the absorption of biotin (a B vitamin). This can lead to skin and hair coat problems. Raw eggs may also contain Salmonella.
Raw fish Can result in a thiamine (a B vitamin) deficiency leading to loss of appetite, seizures, and in severe cases, death. More common if raw fish is fed regularly.
Salt If eaten in large quantities it may lead to electrolyte imbalances and kidney problems. Large breeds of dogs that eat salty food may then drink too much water and develop bloat, which is fatal unless emergency treatment is given very quickly.
String Can become trapped in the digestive system; called a "string foreign body."
Sugary foods Can lead to obesity, dental problems, and possibly diabetes mellitus.
Table scraps (in large amounts) Table scraps are not nutritionally balanced. They should never be more than 10% of the diet. Fat should be trimmed from meat; bones should not be fed.
Tobacco Contains nicotine, which affects the digestive and nervous systems. Can result in rapid heart beat, collapse, coma, and death.
Tomatoes Can cause tremors and heart arrhythmias. Tomato plants and the most toxic, but tomatoes themselves are also unsafe. (All parts of the plant except the tomato itself are also poisonous to humans.)
Walnuts Walnuts are poisonous to dogs.
Xylitol Diet products containing the sweetener Xylitol can cause a sudden drop in blood sugar, resulting in depression, loss of coordination and seizures. Unless treatment is given quickly, the dog could die.
Yeast dough Can expand and produce gas in the digestive system, causing pain and possible rupture of the stomach or intestines.