Stalin, Hitler, Mao and others are good examples of dictators. The problem is, they are utterly obsolete. They ruled in times of paper newspapers. TV owner at their time were a minority, and the only way to quickly brainwash their nations was radio.
If we talk about the present and future, there is no need for killing dissidents on the spot. The truth is, people always tend to believe what they are told, and it's enough to tell them you want over all TV channels. If there is no publicly voiced alternate point of views, the several hundreds of dissidents can't do absolutely anything. People around them will believe what they are told by the government, and dissidents will be ignored. They won't be killed: killing creates martyrs and urges their friends and relatives to take revenge. They'll be simply shut up by other non-lethal means, for one, by restricting their access to public media. You can take modern Russia and China as model examples.
Orwell wrote a great book. Read his "1884". He perfectly demonstrated how "external enemies" can be blamed for internal problems.
So a totalitarian society of the future would be a mix of powerful public media and a police state that suppresses all attempts to voice real peoples' concerns in public (like public demonstrations or articles in the mass-media). There will be no mass executions and big concentration camps, such a system is dangerous for the dictator himself and his cronies in the first place (read about the history and evolution of the USSR in 1950s-1970s). Conflicts of ruler's interests will be inevitable, but all the dogfighting will be done under a carpet. General public won't see it.
I thoroughly recommend "A Day In The Life Of Ivan Denisovich" mind shattering. Some graphic violence in it though, including rape.
It can be a shock for people living in Western countries. However, this description of the Soviet penitentiary system is incorrect. The story was published in the USSR in 1960s during so-called "the Thaw". While it was possible to publicly discuss such things at that time, even then authors couldn't tell all the truth. In fact, Solzhenitsin was blamed by many Russian dissidents of coloring the truth. The reality was much more terrifying. People were shot on the spot just out of a whim of a guard. Hundreds and thousands of them died due to starvation and cold. Sometimes prisoners of labor camps consumed bodies of their dead inmates, and so on. The entire country was terrorized - and in the same time many people sincerely believed that they were building better and brighter future for the entire humanity. Such a mix of feelings and emotions can't be imagined by anyone who didn't live at that time.