Whenever you kill a Spotty Bulbear and its babies. Bonus if you don't use the Ultra Bitter-Spray, and/or fight it with only the captains.
The YouTube user Himajin's 'Perfect Pikmin' run of the first game deserves a special mention. Not only did he manage to beat the game in six days without hacking, a feat that was though to be outright impossible, he did it all without losing a single Pikmin!It has to be seen to be believed.
Louie making it all the way to the bottom of the Dream Den was pretty cool of him, considering that the dream den is the hardest dungeon in the game and some of the passages to the next floor are blocked by stone.