TVP - textured vegatable protein (you buy it dry and rehydrate it with water and then use it as a ground beef substitute in sauces and casseroles
Tofu - chopped fine it takes on the flavor of what you're cooking and disapears into the dish
Quinoa - a south american grain that is high in protein (use it like you would rice)
Legumes (beans, peanuts, lentils, chick peas)
Peanut or almond butter
Eggs
Tuna
I do alot of meat alternatives because I have one vegetarian and two pescetarians (no meat but eat fish). It's really not that hard once you get rolling.
I found the hardest part was to retrain my brain to understand that a meal can be complete without meat on the plate.