I second this list. Theory, as you know, doesn’t just come from Marx, Lenin, and their contemporaries; theory is constantly being developed and refined. Marx and Lenin were, of course, brilliant theorists in their own right, but reading only their works will never give us a full picture of our current material conditions. Here are some works that I recommend that weren’t on the original list and are more recent:
Settlers by J. Sakai. Being primarily a history book, you don't necessarily need a deep understanding of Marxism to understand its thesis, but it's an absolutely necessary read to get a better grasp on settler-colonialism and its relationships.
Trans Liberation by Leslie Feinberg. The gender and liberation movements are central to Marxism, and Feinberg brilliantly shows the connections between the movements and the wider proletarian movement.
Socialism with Chinese Characteristics by Roland Boer. A wide-encompassing book that looks at the political economy, culture, and history of China. One of the most important features of this book is how Boer firmly explains what classes are and how socio-historical conditions shape them.
Elementary Principles of Philosophy by Georges Politzer. This book goes through materialism, idealism, dialectics, metaphysics, and the broad history of these philosophies. Most importantly, it shows how to put into practice the dialectical method and why it's important.
Political Economy: A Beginner's Course by A. Leontiev. This book goes through the most important aspects of Capital volumes 1-3 and Imperialism, the Highest Stages of Capitalism.
I second this list. Theory, as you know, doesn’t just come from Marx, Lenin, and their contemporaries; theory is constantly being developed and refined. Marx and Lenin were, of course, brilliant theorists in their own right, but reading only their works will never give us a full picture of our current material conditions. Here are some works that I recommend that weren’t on the original list and are more recent: