Sebastiano Timpanaro did investigate the relationship between Giacomo Leopardi and d’Holbach in the Italian preface to the latter’s book “Good Sense”. Clearly, d’Holbach was just a broadcaster of the doctrine the Portuguese-Dutch thinker had previously elaborated. The Portuguese-Dutch thinker was behind some of the most radical propositions of Western materialism. Giorgio Colli once complained that no sign of the presence of Spinoza is detectable in today’s debate.
Things have changed, and radically.
Besides the books that Antonio Negri wrote in jail about him,
two very interesting recent books about Baruch Spinoza have appeared
While Damasio’s book is a poetic rumination on how much of today neuroscience can be read amidst the pages of the Jewish thinker, Israel’s book is a solid scholarly work, where the author advances the thesis that it is Spinoza the real engine of most of the Enlightenment radical ideas that we now take for granted, Democracy, free thought and expression, religious tolerance, individual liberty, political self-determination of people, sexual and racial equality etc.
Karl Löwith also wrote on Spinoza: here a review (in Italian)
As an aside, as regards Heretics and Socinianism, Francesco De Sanctis (in Storia della Letteratura:pgg. 283ff.), Delio Cantimori, and later Adriano Prosperi investigated the link of their ideas to the modern concepts of democracy, equality etc.
Compare this very nice blog, in this article.
Apropos Muntzer and his reign, see Luther Blissett “Q”.
A source of ideas is also: this book by Igor Shafarevich on Socialism.