I've also heard that grapes are bad. Here's a quote from this site...

[According to recent research, including a soon to be published study from the ASCPA Animal Poison Control Center in Urbana, IL, grapes and raisin are toxic to dogs. "We've documented that eating grapes and/or raisins can cause renal failure in dogs," says the veterinary toxicologist Dr. Steve Hansen, who is the executive director of the Animal Poison Control Center. "What we don't know is why. It might be a pesticide, or maybe a mold that occurs (on the skins of grapes and raisins)."]

Here's a forum/thread that list some foods not safe for dogs.
http://www.boxerworld.com/forums/showthread/t-42977.html