Here is a list of poisonous foods for cats. I just found this. It's not complete though. I've heard Garlic and Chocolate are also very poisonous. Just thought I'd mention it. One time my younger kitty got into chocolate and I called the vet and they had me bring him in and they gave him something to make him throw up to get the chocolate out of his tummy. He didn't throw up until I got home and all over the place.
Apple seeds
Apricot seeds/pits
Avodaco fruit/pit
Cherry (the whole thing)
Eggplant (the greens)
Elderberry
Mushrooms
Onion
Potato
Rhubarb (leaf)
Tobacco
Tomato (greens)