The Bad -
Many bulb vegetables are poisonous to dogs. Garlic, onions, shallots, chives and leeks all contact N-propyl disulfide, which can cause the destruction of red blood cells and lead to anemia.
All parts of avacado contain persin (sp?) and are dangerous to dogs.
Mushrooms are another sometime toxic veggie.
Grapes and rasins contain toxins known to cause kidney failure.
Corn cobs not a good idea because of bowl obstruction, same for fruits with pits, or large seeds. Apple seeds are also toxic to dogs.
The Good-
broccoli, carrot, sweet potato, squash, celery, beets, spinach ,cabbage, pumpkin, raspberries, blueberries, bananas, pears, mangos, pineapples, apricots, peaches and strawberries. I'm unsure about tomatos as I read conflicting things. Lettuce I'm also unsure about.