Frozen spinach is wonderful. It's cheap (about $0.90/brick), good for you (Hello, Iron!), and looks neat when you mix it with other foods. Plus, it's pre-chopped, so all you really have to do is defrost it and throw it into whatever you're eating, whether that's pasta primavera, potato soup, enchiladas, white sauce...you name it, frozen spinach probably makes it better.
The one downside of frozen spinach is that it doesn't really have any taste and it would probably make an atrocious side dish. But when added to something that already tastes good, it's fantastic.