Candy (contains Xylitol, a deadly substance that leads to liver failure)
Ice Cream
Chocolate (causes diarrhea, tremors, seizures, and death) 
Any processed, cooked, baked, etc. human food
Guinea pig food
Dog food
Any food meant for a species other than rabbits
Yogurt drops from pet stores
Pretty much any treat sold at Petco or Petsmart
Colorful gourmet rabbit chow mixes sold at big-name pet stores
Iceberg lettuce
Nuts
Most seeds
Cherries (the actual fruit is not poisonous except for the pit, but I wouldn't risk it)
Any fruit pits or seeds
Peas
Corn
Avocado
Spinach
Rhubarb
Eggplant
Potato
Grapes
Raisins
Bread
Most cereals
Onion
Garlic
Chives
Rice
Dairy products
Chips
Wild carrots
Tomato plant