Here is a fun little story of how I discovered a nice combinatorial identity when I was an undergraduate student intern at Stanford in the summer of 2007.
Update: I posted this identity on the Piazza for the CS70 class in Berkeley Spring 2013 for a prize money of $100. It was successfully solved by one of the students and there was substantial effort put by many other students. Through this process, I ended up learning many different proofs of this identity! :)