Although Benevolent may be somewhat of an overstatement, Caesar was regarded as a fantastic dictator by the plebs of Rome. To those in the patrician class, Caesar was a tyrant, and hated. But Caesar was fantastic to the people. He reduced tax and solved lots of people's problems at the time. When he was killed on the senate floor, Brutus and Cassius realised they hadn't helped Rome by organising his murder. Instead they very nearly plunged Rome into a second civil war. In his will, Caesar gave each meme br of Rome money enough to live on for a week or two, which furthers my point. Although he didn't acquire his title conventionally, he was missed by the Plebs of Rome after his assassination. ( he was stabbed 27 times which was also a bit of overkill). Hope this helped :)
This is a hard question to answer for sure because it's hard to define precisely what constitutes a "dictator". Also, no matter what a leader of a country may do, they are almost certain to face some opposition to their actions from somebody, so one would be hard pressed to find any (modern) examples of leaders who are universally regarded as benevolent.
The Romans had a system for installing dictators where, in times of great crisis, the senate could nominate a dictator for a few months to solve the republic's problems and then renounce power as soon as the crisis was over. [Cincinnatus] (http://en.wikipedia.org/wiki/Lucius_Quinctius_Cincinnatus#Dictator) was nominated as dictator in 439 BC when Rome was attacked by the Aequi. The senate found him on his farm, where he was told that he had been made dictator. He travelled to Rome that day, called up the army, defeated the Aequi and then immediately stepped down, only fifteen days after becoming dictator.
With that being said, you are probably more concerned with the modern meaning of the word "dictator". The closest example that I can think of would be Singapore's Lee Kuan Yew . He is hailed for his transformation of the country under his rule, from a third world country to the Asian tiger that it is today, but also denied his citizens many civil liberties and hardly enforced his laws.