According to this article, several foods aren’t safe for dogs or cats:
The veterinarian group also warned that many common foods are not safe for pets, including salt, garlic, onions, grapes and chocolate.
http://news.yahoo.com/s/ap/20070404/ap_on_re_us/homemade_pet_food;_ylt=AjXwOQmDn7pRADsbWYs6Mbis0NUE
I agree on all but the garlic... you have to give a whole lot of garlic to cause problems and I’ve fed garlic for years to my dogs.