Several of the novels of Sinclair Lewis: Babbitt, Elmer Gantry, Main Street, and It Can’t Happen Here. They showed a side of America that goes against it’s wholesome, freedom-loving self-image.
Howl, by Allen Ginsberg. This poem is a Beat era classic, taking poetry out of its comfort zone and daring to show its dark underbelly.
Leaves Of Grass by Walt Whitman. His poems have a feel and an energy in them, like you’re actually walking through the woods; he is also upfront with his homoerotic love, which was dangerous to express in that era.
The Other America by Michael Harrington. Harrington shows a portion of America that has not benefitted from any “prosperity” happened; it is also a call to action.