Marx and Engels, The Communist Manifesto (1847), chapter 3 “Critical-Utopian Socialism and Communism”
Ernst Bloch, The Spirit of Utopia (1918), chapter 1.3 “The Shape of the Inconstruable Question”
Michel Foucault, “Of Other Spaces: Utopias and Heterotopias” (1967/1984), trans. Jay Miskowiec, Diacritics 6, no. 2 (Spring 1986): 22-27 (also available here); “Des espaces autres,” in Dits et Écrits, vol. IV, 1954-1988, eds. Daniel Defert, François Ewald, and Jacques Lagrange, 752-762 (Paris: Gallimard, 1994).
Fredric Jameson, Archaeologies of the Future: the Desire Called Utopia and Other Science Fictions (Verso 2005), Chapter 10 : Utopia and Its Antinomies
Zapatista Army of National Liberation, Sixth Declaration of the Selva Lacandonia (2005)
Erik Olin Wright: Envisioning Real Utopias (Verso 2010): Chapter 6. Real Utopias I: Social Empowerment and the State ; Chapter 7. Real Utopias II: Social Empowerment and the Economy
Alex Williams and Nick Srnicek, Manifesto for an Accelerationist Politics (2013)