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Although it has already been stated in a casual way, combining grains with beans will give you a complete protein source. Most confuse the issue with numerous specific recommendations, but if you simply remember grains + beans, you can choose your own combos of food items.

Proteins that humans eat are broken down into little pieces called amino acids which your body then uses to make its own proteins. There are about 20 of those amino acid building blocks that are used by humans to make new proteins that they need. Eight (8) of those building blocks can only be gotten from your food. The rest your body can make from other stuff and you don't have to worry about usually.

Those 8 "essential amino acids" are fully provided by any meat, egg or dairy product, but can also be obtained by combining grains with beans in a person's diet. That is why much of the third world subsists on beans and rice. It is one of the most nutritious meals you can make for the least amount of money.

There are a few grains that provide complete sources of essential amino acids, and are therefore complete protein sources, but they are rare in most western diets (and supermarkets): quinoa, buckwheat, hempseed, and amaranth. I can get quinoa from a nearby health food store, and I like it, but it is not as cost effective as beans and rice.

I also thought tofu was a complete protein, but I was just reading in wikipedia that it's contested as a complete source. Regardless, if you add any grain to that, it definitely is a complete source.