the bad list

First thing is first... the foods to avoid.

ALWAYS, ALWAYS check your food labels... even if it states it's gluten-free. Sometimes a label will state something is gluten or wheat-free... but in the small type will say something like "made in a facility that also processes wheat" or "made on equipment shared with wheat".

The obvious:
bread
bagels
pasta
cookies
most cereals
cakes
oatmeal (unless specifically labeled gluten-free)
wheat
barley
rye
flour

The not so obvious:
spelt
matzo
kasha
soy sauce
msg
modified food starch
malt
thick sauces (usually thickened with flour)
gravies
chicken broth (check ingredients)
beer
bread crumbs
fried foods coated with flour
french fries (often coated with flour)
imitation crab meat (check your sushi!)
vegetarian - veggie burgers, soy burgers, imitation meat, etc (often held together by gluten)
some medications - check with your doctor or pharmacist