Consider Ellison's posthumously published book Juneteenth.
Invisible Man is a classic of African-American literature. Consider reading the work of the theorists who preceded him, such as W.E.B. DuBois and Booker T. Washington, and the work of Harlem Renaissance authors, such as the poetry of Langston Hughes and Their Eyes Were Watching God by Zora Neale Hurston. Consider also Ellison's contemporaries, Richard Wright (Black Boy and Native Son), James Baldwin (Go Tell It on the Mountain and Giovanni's Room), and Gwendolyn Brooks (Blacks).
Consider also some of the writers besides Wright whom Ellison named as influencing him, such as Mark Twain, Saul Bellow, William Faulkner, Fyodor...