There are so many good choices here already. I'll select two that haven't been mentioned yet.
The Reformation gave a death blow to the Dark Ages and the stifling influence of the Catholic Church. Without the Reformation science would still be shackled by Roman theology and the Western theocracy would be as bad as anything any ranting mullah ever dreamed of.
The Renaissance blew through Europe like a fresh breeze, bringing all manner of new knowledge in the arts and sciences.