[mudling]

Have only played fairly recent games so I'll mention these:
Ditto the first two of Anonyman!'s list.
COD 4- All Ghiled up, when the army sneaks past you.
Mass effect- A certain choice on a certain planet about which party member you have to leave behind.
Halo 3- The battle between two scarabs
Pokemon (Blue version)- Obtaining your pokemon (I was like 7 when I first played this, and everyone I knew did it too, it brings back memories, along with captain planet.
Portal- Fight with GLaDOS and ending sequence
Half life two- Retaking city 17 (I was bored of this game, and stumbling through, and then It just got so much better from Nova prospect onwards, and having the rebels running around you and destroying giagantic tripods was great)
I'll add more later.