I will give you two:
The first is Winston's first encounter with Julia where they meet and go off into the country in order to have sex. He finds it to be exhilirating physically but also because he feels it is an actual act of defiance against big brother, that in their coupling they are working together to bring down the Party in a way.
The second is the discovery of the journal. Though it is referred to only as something that happened prior to our entry into the narrative, it is obviously one of the most important things that happened to Winston and he sees it as the place where he actually starts being able to analyze his motives and think about his place in the world more than he did prior to its discovery.