Chocolate
Most people are well aware that chocolate poses a real risk for dogs. Please remember that the darker the chocolate; the more toxic it is for your dog. Chocolate in low-doses may cause vomiting and diarrhea, bu in high-doses can lead to heart palpitations and neurological diseases. There is no cure for chocolate toxicity, but rapid diagnosis and supportive care can help save your dogs life.
Raisins
Grapes in general are toxic to dogs and cats, and raisins being concentrated grapes are particularity harmful. Acute kidney failure can occur if enough raisins have been ingested. Kidney support with IV fluids may help, but the kidney failure could be permanent.
Onions/Garlic
Dogs and cats will develop severe vomiting and diarrhea if enough onion/garlic is eaten. The real problem occurs hours to days later when oxygen carrying red blood cells are destroyed by the toxins in the blood. Oxygen therapy and even blood transfusions may be needed.
Xylitol
This artificial sweetener found in some low-calorie candies and foods can be very dangerous in dogs. It hides silently in many peanut butter brands that advertise as being low in sugar. Xylitol tricks the dogs body into releasing insulin which in turn lowers the blood sugar to dangerously low levels. Dogs will become weak and may pass out. Aggressive IV fluids with added sugars are needed to counteract the xylitol.
Bones
Although not truly toxic the ingestion of bones can lead to profound consequences. If not adequately chewed and digested by the stomach fragments on the bone may become lodged in the small intestine. This alone can cause an obstruction requiring emergency surgery. If the bone fragments are sharp enough they may even puncture the bowel leading to severe and life threatening infections. Poultry bones like chicken and turkey tend to splinter when chewed and may be the worst offenders.
This list is by no means complete and if you ever think your pet may have eaten something toxic or dangerous (like bones) please contact your veterinarian or the ASPCA poison hotline at (888) 426-4435.