Aspartame (NutraSweet): Artificial sweetener. Italian research in animals indicate that long term consuption may increase risk of leukemia, lymphoma and breast cancer. Some people report dizziness, hallucinations, headaches after drinking diet pop. People with PKU need to avoid aspartame.
Saccharin: Animal studies indicate that it can cause cancer of the bladder, uterus, ovaries, skin and other organs. It also seems to increase the potency of other carcinogens. Can not be sold as an ingredient in foods or beverages in Canada.
Sodium Nitrate, Sodium Nitrite: Adding this to foods can cause small amounts of potential cancer-causing chemicals called nitrosamines.
Information Source: Nutrition Action
Want help remembering what chemicals to avoid check out my quick guide to chemical additives.