Onions, in large quantities or with continued feeding, can cause a type of anemia in dogs.
I wonder about grapes and raisins, as it is only recently that vets have taken note of their toxicity, if it isn't the pesticides rather than the fruit. i know that raisins and grapes are some of the most treated fruit, that is to say they have very high levels of chemicals on them. Not that I'm going to test my theory by giving my dogs organic raisins, I just wonder about it.