Hmm...

-Defeating Dracula in the original Castlevania...about eight years after I first got the game.

-Defeating Kefka in FFVI for the first time, with Locke and Strago on their last legs after barely surviving Ultima because I was horribly under-leveled.

-Capturing Mewtwo in Pokemon Red with Ultra Balls when my 6th pokemon was barely alive.

-Defeating Ozma on the 50th try.

-The end of Bart vs. The World. Come on, people. You gotta love being able to torment your arch foe in a game like that.

My next great moment likely will come when I figure out how to open treasure chests in Unlimited Saga...