Apple Seeds (contain Arsenic)
Apricot, Cherry and Peach Stones
Avocado (all parts)
Chewing Gum (contains xylitol)
Chocolate - all kinds (contains theobromine - can cause death)
Coffee and Tea (contains caffeine)
Grapes, Raisins and Sultanas
Green/Sprouting Potatoes (i.e. unripened)
Onions (lots of foods contain onion powder)
Turkey Skin (can cause pancreatitis)
Almost all cleaning products (bleach, scrubs, sprays, etc.)
Fuels (petrol/diesel etc.)
Nail Varnish (+ Remover)
Paints and Stains
A wide range of indoor and outdoor plants are poisonous to dogs. Avoid allowing your dog to eat any plants to be on the safe side.
These are not exhaustive lists. Always err on the side of caution and consult a vet if you are concerned.