As for some Red China stuff, in the Western mainstream there's Bertolucci's Oscar-winning epic The Last Emperor (1987)
and Marty Scorsese's Kundun (1997)
that both show some of the transition to and effects of the Communist State. A terrific drama from this century that looks a bit at the modern Chinese system and culture is Yimou Zhang's Riding Alone for Thousands of Miles - 千里走单骑 (2005)
, though it doesn't address Communism overtly.
Going down Southeast Asia, there are some good flicks about Cambodia's transition to a Communist State under Pol Pot's Khmer Rouge in the 1970s, The Killing Fields (1984)
, Spalding Gray's monologue about the making of that film as well as covering some of the history Swimming to Cambodia (1987)
, and the documentary S21: The Khmer Rouge Killing Machine (2003)
which won the François Chalais Award at Cannes.
As for Cuba, there's Soderbergh's recent biopic Che (2008)
starring Benicio del Toro, Before Night Falls (2000)
is a biopic starring Javier Bardem as a Reinaldo Arenas a Revolutionary turned poet and author who was jailed for his homosexuality, and Buena Vista Social Club (1999)
Wim Wenders terrific music documentary that isn't overtly political but does show some of the effects of the Castro years in modern Cuba.