According to the ASPCA, you should avoid feeding or allowing your dogs and cats to eat the following.  If you fear your pet has been poisoned, please call the ASPCA Animal Poison Control Center 24/7 at (888) 426-4435. A $55 consultation fee may be charged.

Foods/Drinks

Avocado
Chocolate (all forms)
Coffee (all forms)
Fatty foods
Macadamia nuts
Moldy or spoiled foods
Onions, onion powder
Raisins and grapes
Salt
Yeast dough
Garlic
Products sweetened with xylitol

 

Warm Weather Hazards 
Animal toxins—toads, insects, spiders, snakes and scorpions
Blue-green algae in ponds
Citronella candles
Cocoa mulch
Compost piles Fertilizers
Flea products
Outdoor plants and plant bulbs
Swimming-pool treatment supplies
Fly baits containing methomyl
Slug and snail baits containing metaldehyde

 

Cold Weather Hazards
Antifreeze
Liquid potpourri
Ice melting products
Rat and mouse bait

 

Medication 
Common examples of human medications that can be potentially lethal to pets, even in small doses, include:
Pain killers
Cold medicines
Anti-cancer drugs
Antidepressants
Vitamins
Diet Pills

 

Common Household Hazards
Fabric softener sheets
Mothballs
Post-1982 pennies (due to high concentration of zinc)

 

Holiday Hazards 
Christmas tree water (may contain fertilizers and bacteria, which, if ingested, can upset the stomach.
Electrical cords
Ribbons or tinsel (can become lodged in the intestines and cause intestinal obstruction—most often occurs with kittens!)
Batteries
Glass ornaments