Obama is referring to there significant intellectual or artistic figures. Each one had previously believed in the power of their conviction and what they could accomplish, but with time they were worn down by focusing on the negative aspects of being African American, rather than a strong and empowering sense of identity.
Placing this within the context of Obama's life at this point, he is searching for a way to understand his own social (and racial) identity. He turns to these famous texts to understand himself, but finds they focus on the problems of being African American (the "corrosive force" and "self-contempt" that he mentions), rather than the positive sense of strength that he needs.
James Baldwin was a famous African American and gay author. Many of his stories include themes of self acceptance in the face of strong social forces. Eventually, he left the United States to live in France to avoid the racism and homophobia had experienced.
Langston Hughes was a poet. He grew up in the midwest (Kansas) and spent his younger years traveling. Many of his poems and other works are based on his travels, as well as his cosmpolitan interest in the Black experience across the world. Later he would life almost entirely in Harlem as a part of the Harlem Renaissance.
Du Bois was an intellectual and social scientist who, among many other things, helped found the NAACP. Especially in his early speeches and writings, he emphasizes the need for full civil, social, educational, economic, and other rights for African Americans. Later in life, he would leave the NAACP and instead advocate for compromises, but not authentic acceptance of African Americans in society (such as "separate but equal" policies). Near the end of his life he left America entirely to live in Ghana.
Obama contrasts all three with Malcolm X, who he felt embraced this identity as a positive creative force:
Only Malcolm X's autobiography seemed to offer something different. His repeated acts of self creation spoke to me; the blunt poetry of his words, his unadorned insistence on respect, promised a new and uncompromising order, martial in its discipline, forged through sheer will.