Many fresh fruits and vegetables are wonderful for dogs. Vegetables such as broccoli, green beans, peas, spinach, zucchini, string beans, corn, carrots, etc are excellent. Avoid avacodoes and remember fruits are sugary and in excess can lead to diarrhea.
Dr Carol Osborne, DVM
Grapes are definitely toxic for dogs. NO grapes! Raisins are the same, ditto sultanas, currants, etc. I've heard of dogs who like bananas, but mine doesn't.
Corn....well I know it's basically good for them, but I would break up or mash up the kernels first. Because dogs won't chew it like humans do, they haven't got that kind of teeth. It will come out the other end exactly the same as it went in! And there's no nutritional value in food that does that. The kernels of corn have quite tough "shells" around them, and they won't get broken down in the digestion.
In fact, I won't give corn to my dog anymore, because she once ate some, and because it was indigestible it upset her belly quite badly.
However, the nutritional value of corn for dogs is good, so long as it is crushed or broken first.