20th century's worst
20) Josef Mengele (6)
17) Hideki Tojo (8)
17) The Rosenbergs (8)
17) Adolf Eichmann (8)
14) Benito Mussolini (11)
14) Ayatollah Khomeini (11)
14) Emperor Hirohito (11)
13) Ho Chi Minh (13)
12) Kim Il-Sung (14)
10) Kim Jung Il (15)
10) Fidel Castro (15)
9) Osama Bin Laden (18)
8) Idi Amin (21)
6) Yasser Arafat (24)
6) Saddam Hussein (24)
5) Vladimir Lenin (28)
4) Pol Pot (31)
3) Chairman Mao (35)
1) Joseph Stalin (39)
1) Adolph Hitler (39)
Honorable Mentions: Kaiser Wilhelm II (4), General Suharto (4), Richard Nixon (4), Slobodan Milosevic (4), Mengistu Haile Mariam (4), Lyndon Johnson (4), Alger Hiss (4), Heinrich Himmler (4), Hillary Clinton (4), Neville Chamberlain (4), Robert Mugabe (5), Bill Clinton (5)
This list is from Right Wing News. I would like to see a similar list from the left is there is such (maybe you could start one here)
Off hand, not counting the honorable mentions, it seems to be a pretty good list. I might have left off Hirohito, Lenin and Ho Chi Minh.