Celiac disease (aka celiac sprue, nontropical sprue, and gluten-sensitive enteropathy) is a digestive disorder that causes affected individuals to have an immune-system reaction to gluten (protein).  Gluten is found in wheat, both whole wheat and white, seminola, durum, spelt, kamut and faro, rye and barley.  You should be careful about oats. Try to get the oats that are certified gluten-free.  Bob's Red Mill makes these, get them at the health food store.  The Irish oatmeal McCann's does not guarantee theirs to be gluten free.

The reaction triggered by the gluten damages the small intestine and prevents it from absorbing nutrients, which can lead to vitamin deficiencies that harm the brain, nervous system, bones, liver, and other organs, as well as stunt the growth of children with the disorder.  Symptoms of celiac disease make it difficult to diagnose, as they can be vague and hard to pinpoint.  Some of these include diarrhea, bloating, abdominal pain, fatigue, unexplained weight loss or gain, and unexplained anemia. Other symptoms include mood changes, fatigue, bone or joint pain, itchy skin rashes, muscle cramps, osteoporosis, and/or tingling numbness in the legs.   Gluten intolerance is also associated with fibromyalgia. 

According to the Celiac Disease Foundation, 1 in 133 people are afflicted with the disorder.  Some sources put the number at 1 in 100 people.  Whatever the number, nearly 97% of them go undiagnosed. 

Undiagnosed celiac disease can lead to premature death, and also contribute to a low quality of life.  

Besides the flours/grains mentioned above, here are some other products/foods that contain gluten. 

Bulgur
couscous
farina
faro
graham flour
matzo meal/flour
malt or malt flavoring (usually made from barley)
malt vinegar
orzo
panko
seitan
triticale
hydrolyzed wheat protein
beer and grain-based alcohol
brown rice syrup
caramel color
dairy substitutes
dextrin
dry roasted nuts
gravy
some herbs
hydrolyzed vegetable protein
imitation seafood
licorice
lipstick, gloss or chapstick
lunch meats
modified food starch
postage stamps
salad dressings
canned/packaged soups
soy sauce
some vitamin supplements
toothpaste

For a complete list google gluten containing products and there are many websites dedicated to celiac that will list these.

You look at this list and you say "what's left?'   Well, here are some of the foods that you can consume.

Amaranth
Arrowroot
Buckwheat
Cassava
Corn
Flax
Chickpeas
Indian rice grass
Job's tears
Legumes
Millet
Nut flours
Potatoes
Quinoa
Rice
Sago
Seeds
Soy - but I don't recommend this
Tapioca
Teff
Wild rice
Yucca
Meat - unprocessed
eggs
fish - avoid farm raised
dried peas, beans, peanuts
fruit
vegetables
milk and milk products
coffee, tea, soda, wine gin, rum,
olive oil
sweeteners

Remember, it will take some work to convert your diet to gluten free, but the benefits will far outway the trouble.