Here are some guidelines for steering clear of GM foods in your diet:
Soybeans - Gene taken from bacteria (Agrobacterium sp. strain CP4) and inserted into soybeans to make them more resistant to herbicides. http://en.wikipedia.org/wiki/Soybean#Genetic_modification. See How to Live With a Soy Allergy for more information on avoiding soy products.
Corn - There are two main varieties of GE corn. One has a Gene from the lepidoptera pathogen
microorganism Bacillus thuringiensis inserted to produce the Bt toxin, which poisons insect pests. http://en.wikipedia.org/wiki/Soybean#Genetic_modification. There are also several cases which are resistant to various herbicides. Present in high fructose corn syrup and glucose/fructose which is prevalent in a wide variety of foods in America.
Rapeseed/Canola - Gene added/transferred to make crop more resistant to herbicide.
Sugar beets - Gene added/transferred to make crop more resistant to Monsanto's Roundup herbicide.
Rice - Genetically modified to resist herbicides; not currently available for human consumption, but trace amounts of one GM long-grained variety may have entered the food supply in the USA and Europe. http://www.cfsan.fda.gov/~lrd/biorice.html
More recently, golden rice, a different strain of rice has been engineered to produce significantly higher levels of beta carotene, which the body uses to produce vitamin A. Golden rice is supposedly still undergoing testing to determine if it is safe for human consumption. http://news.bbc.co.uk/1/hi/sci/tech/4386933.stm
Cotton - engineered to produce Bt toxin. The seeds are pressed into cottonseed oil, which is a common ingredient in vegetable oil and margarine. Both should be avoided.
Dairy - Cows injected with GE hormone rBGH/rBST; possibly fed GM grains and hay.
Aspartame/AminoSweet - Addictive and dangerous artificial sweetener commonly found in chewing gum and "diet" beverages. A building block of aspartame, the amino acid phenylalanine, is usually manufactured with the aid of genetically modified E. coli bacteria. This process has been used industrially in the USA for many years.
Farm Raised Salmon avoid.