When I was 7 or 8 (I forget which) I got Yoshi's Island for the SNES. When I reached the end where you fight Baby Bowser I easily beat him and thought that was the end of the game. Then there was the scene where you are ontop of the castle and you see these yellow eyes light up in the shadows and the music starts. Bowser slowly gets up and he was huge and did the roar thing. Since I was so young I marked out for the first time and never have I marked out at a game since.
Ontop of that when he started charging towards me, I paniced and was marking out more.
A vid of it I found:
http://youtube.com/watch?v=LtKh7e2ESBc
When your 7 and thats the best thing you have seen on a videogame then its pretty exciting.
Another good memory is making my sister sick when she was lying on the couch,ill, I played Raphael Ravens Moon level in front of her and made the screen spin around over and over again.