I think the most defining moments were:
1. When Woody persuaded the Mutant Toys to save Buzz from Sid because he told them he was his friend and afterwards, the two toys shook hands.
2. When Buzz decided to go save Woody after Al kidnapped him, despite it being dangerous; "Woody once risked his life to save me. I couldn't call myself his friend if I weren't willing to do the same."
3. Woody saying to Buzz: "For Infinity and Beyond!"
Will Barbie and Ken return?