Thus Always to Tyrants?

I'm just catching up on some of the Guy Fawkes commemorative TV from last week. The BBC's Timewatch had an interesting programme devoted to the Gunpowder Plot, which argued that even if the conspirators had been successful in killing James I and the English political elite then the only likely result would have been a wave of anti-Catholic pogroms across the country - that England would have emerged from the chaos a more, rather than less, Protestant country than it already was. Which made we wonder: has there ever been a political assassination which worked, in the sense that it accomplished the long-term goals of the killers? (I'm obviously not counting a 'successful' assassination as one in which the target merely dies. Also, I'm talking specifically about the violent and sudden doing-away-with of the head of government, rather than terroristic attacks in general).