Don't forget legumes!! Beans, beans, beans! Great sources of protein and inexpensive. Try putting different kinds of beans in your soups and pasta sauces...kidney, cannelini, pinto, black, garbanzo, navy....etc. They come already cooked in cans or you can get them dry and add to soups according to package directions.
Garbanzo beans are the primary ingredient in hummus. Make your own or buy lowfat versions for pitas and crackers....load the pita with hummus and veggies.
Also nuts....add cashews, almonds, etc to your snack ideas. They are loaded with GOOD FAT and protein, but don't go overboard....keep them to the recommended serving as they are also high in calories.