This is the case that syntactically is used for subjects. In English, pronouns are inflected for case, i.e. the subject pronouns (i.e. I, you, he, she, it, one, we, they). Note that "you" is both the nominative and accusative form in the second person. Generally in English, syntactic function is marked by word order.
Occasionally object pronouns are used in the nominative, notably e.g. "Me and my friend went to the park". We need an article on this, somewhere... how about nominative me