It is difficult to find good documentaries on communism on the internet not because they aren't there but because they keep on getting removed by parties not wanting it fully exposed. The following movie was made by a Muslim academic from a Muslim perspective and so reflects a religious bias. However, of you ignore this and focus on the history, you will find this an eye-opener.
If, however, you can get a copy of The Soviet Story this is without doubt the best and most exhaustive of the documentaries on the subject. Extracts and sometimes the whole movie can be found on YouTube.
Communism was the bloodiest of the atheistic ideologies (worse than fascism) that caused more than 120 million innocent deaths in the 20th century. It was a nightmare which promised equality and justice, but which brought only bloodshed, death, torture and fear. This four-volume documentary displays the terrible savagery of communism and its underlying philosophy. From Marx to Lenin, Stalin, Mao or Pol Pot, discover how the materialist philosophy transforms humans into theorists of violence and masters of cruelty.