Books

The Marxists Internet Archive has a huge amount of left/communist non-fiction. It's very broad in its scope, so there's Stalin and Mao on there alongside William Morris and HG Wells. You could also check out Timothy Snyder and Rebecca Solnit, who both had interesting books about resisting fascism from a more contemporary viewpoint.

In fiction, there's The Man in the High Castle, by Phillip K. Dick, which has a similar alt history concept as Roth's The Plot Against America. And of course there's George Orwell's writing, both fiction and non-fiction, much of which explores the nature of fascism. I'd also recommend Isabel Allende's The House of the Spirits, if you like magical realism.