Playing in the DarkPlaying in the Dark by Toni Morrison
This is one of the most insightful pieces of literary criticism that I have ever read. It's very accessible, the ideas are not couched in academic language. The ideas of the piece are simple but powerful. It's brief (three chapters). If I had to make a list of the books that impacted me the most, this book would be in my top ten.
This book is a look at racism in various works of fiction. It looks at the minor characters -- the servants in the background, the savages who appear briefly only to be killed by the white protagonists, the slaves who never speak -- and demonstrates that these characters are in fact central to the story.