Anti Freeze Acute cases of antifreeze toxicity can present itself as if an animal is drunk from alcohol. If you suspect your dog has had any antifreeze, it is a life threatening situation and yhou should speak to your veterinarian immediately.
Apple and Apricot seeds These seeds contain cyanogenic glycosides which can result in cyanide poisoning.
Avocado Avocado contains persin which can damage heart, lung and other tissue in many animals. They are also high in fat and can cause an upset stomach, vomiting or even pancreatitis. The seed pit is also toxic and if swallowed can become lodged in the intestinal tract where it may cause a severe blockage which would have to be removed surgically. Beware that Avocado is the main ingredient in Guacamole dip. .
Theobromine, found in chocolate, causes different reactions to different dogs and can trigger epileptic seizures in dogs prone to or at risk of epilepsy. The size of the dog will also be a major factor: the smaller the dog, the more affected it is by the same amount than a larger dog. See chocolate toxicity table here
Grapes and Raisins

It is safer to assume that any human medicine is toxic to dogs, as most of them are are. Paracetamol is particularly dangerous as it can lead to permanent kidney and liver damage which may require life long medical treatment. Unless advised to do so by a vet, do not give your dog any medicine that is not designed for dogs.

Even if the active substance within a human medicine is appropriate for a dog, the dose is likely to be very different and doses vary between individual dogs due to their size, breed and metabolic rate.

Asprin - Tylenol - Pain Medications

Nutmeg Nutmeg can give hallucinations when ingested in large doses and has been known to cause tremors, seizures and in some cases death in dogs.
Onions Onions, especially raw, have been shown to trigger hemolytic anemia in dogs
Potatoe Solanum alkaloids can be found in raw green potato skins, and although rare, poisoning is due to solanine which is poorly absorbed. Cooked and smashed potatoes are fine for dogs being quite nutritious and digestible.
Rhubarb Leaves
Salmon Raw salmon - 'Neorickettsia helminthoeca'. The rickettsial organism does not directly infect the dog but is carried instead by a parasite (a flatworm or fluke) called Nanophyteus salmincola through two intermediate hosts - freshwater snails and salmonid fish.

Nanophyteus salmincola are found to infect some species of freshwater snails. The infected snail is ingested by the salmon as part of the food chain. Neither the fluke nor the rickettsial organism are lethal to the fish. The dog is exposed only when it ingests the secondary host - an infected fish. After the dog ingests the fish, the encysted fluke larvae burst and embed in the dog's intestinal tract and the rickettsia are introduced. The cycle continues when ova are excreted in dog feces to infect more snails.

A sudden onset of symptoms occur 5-7 days after ingestion of fish. Initial symptoms include lethargy and anorexia.

In the acute stages, gastrointestinal symptoms are quite similar to canine parvovirus. Nasal and ocular symptoms can resemble canine distemper. If left untreated, SPD has a mortality rate of up to 90%. SPD can be diagnosed with a fecal sample and is treatable if caught in time. Treatment may include supportive hydration, an antibiotic to kill the rickettsial organism, and a "wormer" to kill the parasite. Improvement may be seen in as little as two days.

Tomato Plants Tomatos and their plants contain atropine which can cause dilated pupils, tremors and an irregular heartbeat. The highest concentration of atropine is found in the leaves and stems of tomato plants, next is the unripe (green) tomatoes and then the ripe tomato.
Turkey skin Turkey skin is thought to cause acute pancreatis in dogs.
Walnuts Most nuts are not good for dogs in general as their high phosporus content is said to cause to bladder stones.