If you are not a fan of ricotta cheese, cottage cheese may be the best substitute. It has a similar flavor and less calories than ricotta, but the texture is not quite the same. If you use this substitute, make sure you drain your spinach very well to reduce the amount of liquid in your mix and it may be a good idea to blend your cottage cheese to get a more consistent texture. You could also search for Italian cream cheese in your grocery store's specialty cheese area.