I am very partial to late 19th century anarchists, but 'propaganda by the deed' included both assassinations (which could be ethically justified as part of a larger war) and a small number of random acts of violence against the general public (which I see no serious ethical justification for (x)). While such acts were a fairly small part of 'Propaganda of the Deed', they are an early example of what would be later labeled terrorism (that is, NGOs using indiscriminate violence against civil populations for political ends).
For example: "February 12, 1894 – Émile Henry, intending to avenge Auguste Vaillant, sets off a bomb in Café Terminus (a café near the Gare Saint-Lazare train station in Paris), killing one and injuring twenty. During his trial, when asked why he wanted to harm so many innocent people, he declared, "There is no innocent bourgeois." This act is one of the rare exceptions to the rule that propaganda of the deed targets only specific powerful individuals. Henry is convicted and executed by guillotine on May 21." http://en.wikipedia.org/wiki/Propaganda_of_the_deed
The small number of acts of terror carried out by anarchists likely didn't give us the 40 year work week (xx), anarchists and other radicals organizing did.
x - The fact that these acts of terror were carried out in reprisal for far worse state terror is no excuse. The ends do not justify the means.
xx - The value of assassination is debatable but clearly terrorism was both counter-productive and unethically unjustifiable.