Here is a great article that we found in Cesar’s Way Winter 2010 Magazine …

 
Don’t Feed THAT to Your Dog!
 
Avocado Skin
It can cause vomiting and diarrhea in dogs (and can kill pet birds and rodents).
 
Alcohol
Not just the drinks are to be avoided; you should steer clear of food made with alcohol. The bad effects range from vomiting and diarrhea to death.
 
Chocolate, Coffee, Caffeine
The villain here is a group of substances called methylxanthines. In dogs, they cause vomiting, diarrhea, abnormal heart rhythms, seizures, and – in extreme cases – death. Dark chocolate is more dangerous than white chocolate. 
 
Cooked Bones
They splinter more easily than raw bones, and the shards can become lodged in a dog’s digestive tract. In fact, Dr. Brunori recommends that you do not feed your dog any bones, as they can cause tooth fracture.
 
Grapes, Raisins
The theory that pesticides are the culprit has been debunked. Still, all scientists know for sure is that the fruits in excessive amounts can cause canine kidney failure. 
 
Gum, Candy, Baked Goods, Toothpaste
Many of these contain a sweetener called xylitol, which can cause liver failure in dogs.
 
Macadamia Nuts
They show up in cookies and candy and can cause a wide range of symptoms – from depression to tremors to hyperthermia – that can last up to 48 hours.
 
Milk
Dogs (and other pets) lack the enzyme that breaks down lactose; they can get diarrhea from milk and milk-based products.
 
Moldy Foods
Even in small amounts, they can cause diarrhea, which is certainly unpleasant for pooches. In bigger doses, they can cause seizures, coma, or even death.
 
Onions, Garlic, Chives
Although they’re more of a problem for cats, large amounts can lead to gastrointestinal irritation and anemia in dogs.
 
Salt
Large amounts can cause excessive thirst and urination. There’s also such a thing as sodium poisoning.
 
Yeast Dough
If your dog eats it before the yeast has fully risen (you drop some on the floor, for instance), the results can be catastrophic. As the dough continues to rise, gas accumulates in the dog’s intestines, which can cause them or the stomach to rupture.