Yeah, this is a bit of a odd challenge.
Looking at history Gaddafi being killed is the most recent case of tyrannicide. Depending on your definition tyrannicide happens on a semi regular basis with at least one happening every or every other decade since 1945. If there was to be more tyrants that needed slaying by the people on a semi-regular basis then one would assume that the world would be a much more unstable place, or that the spread of free information is much more wide spread then today.
Also we have seen in several cases across the Middle East during the Arab Spring, and in both Iraq and Afghanistan that the transition from a dictatorship to a democracy and the rule of law is not at all a simple process and not one that generally allows for a benevolent government. Don't take this the wrong way, but it has been my observation that most new democracies also end up being more corrupt and far less stable then the previous dictatorship no matter how terrible the previous dictator was.