This site is a good site on the Russian Revolution. Scroll to end and note Lenin's death and the resulting triumvirate of Stalin, Kamenev and Zinoviev.

This site briefly discusses the workings of the Soviet system and its leaders. Among those discussed are Stalin and his brutal use of police terror as well as Gorbachev and his perestroika plan.

A timeline covering the history of the Soviet Union from 1917 to 1991.