If you're looking for a frozen dinner, you may even find one that's marked specifically gluten-free — Glutino makes some prepared meals, as does Amy's Kitchen. Don't purchase a frozen meal unless it's specifically marked "gluten-free," since most of those that aren't labeled do contain gluten ingredients.
You also may be able to find some prepared foods in the dry-goods section of the supermarket that are marked gluten-free — for example, I've seen "just add water" pre-made Indian or Thai dishes in the ethnic foods section of the store. Thai Kitchen is one brand that makes some gluten-free dishes you could eat as a meal.
Frozen pizza fans have plenty of gluten-free frozen pizza options, including vegan products and some that are gluten-free and casein-free. Many grocery stores stock at least one or two of these — in my local store, they're in the "natural" foods freezer section, which is separate from the regular freezer section.
Canned Soups: A Few Options Available
People new to the gluten-free diet often are surprised to learn that canned soups frequently contain gluten — the flour is used as a thickener, especially in "cream" soup products. However, it's possible to find some canned soups that are gluten-free.
Progresso makes some gluten-free soups, as does Pacific Natural Foods (which packages its soups in boxes, not cans). Some gourmet soup manufacturers, such as Bookbinders Specialties, also make some gluten-free soup options, but you'll have to read labels and possibly make some calls to determine what's safe and what's not.