A few of the more common pet toxins 
See "other resources" for more extensive listings.

Grapes & Raisins - in SMALL amounts can cause kidney failure
Easter Lily Plants
Caster Beans
Cocoa Mulch
Rose combo fertilizer and insecticide - disulfoton
Antifreeze
Dog tick/flea products used on cats
Over the counter medications (NSAID) given to pets
Oleander, Rhubarb , Sago Palms, Certain Mushrooms
Rat Poison - signs may show-up a few days after ingestion
Chocolate 
Ingestion of Human Prescription Medication
Heavy Metals - birds especially
Benzocaine - sun screens
Macadamia Nuts
Sugar Free Gum containing xylitol - in SMALL amounts very toxic