One of the first things that I did after being diagnosed with Celiac disease was to check with my local Kernels to see if I could still eat their popcorn. At the time, all the flavors that they used were gluten-free, but other offerings by the chain contained wheat.
I’m pleased to say that as of September 2011, all of Kernels’ flavors are gluten-free as well as nut-free! Their allergen sheet will tell you which, if any, of the eight most common allergens are present in each flavor. (OneSpot Allergy also provides a handy summary here.) Kernels are very allergy-aware and will work with you if you have other allergies to help you choose a safe product. (See their FAQ page.)
So go ahead, indulge, and eat worry-free!