One of the lightning rods for HUAC was the 1943 movie Mission to Moscow, which was very pro-Stalin (when Russia was our ally). The North Star and Song of Russia are two others.

Prior to the war, Hollywood took great pains to avoid making any political statements and keep the U.S. very isolationist. However, King Vidor's 1934 film Our Daily Bread gives a great look at collective farming with a famous montage sequence that could be right out of an Eisenstein film, and the 1937 film Blockade was a watered down attempt to cover the Spanish Civil War. It was written by John Howard Lawson, who was one of the Hollywood Ten. Clifford Odets is also credited on the script, but like Elia Kazan, he named names and cooperated with HUAC, which he later regretted.

The 1953 movie Salt of the Earth, about a real life zinc miner's strike, is kind of the poster child for communist filmmaking in America. Director Herbert Biberman was one of the Hollywood Ten and served 6 months in jail. He formed the Independent Productions Company with other blacklisted filmmakers to produce Salt of the Earth, which used real workers to tell the story. You can read more about it here.