From Halopedia, the Halo wiki
I do just love Halo
Gotta love all the Pixar movies
Parks and Recreation, The Office, Avatar: The Last Airbender
Master Chief jumps out of Cairo Station with the covenant nuke. Dude, can it get much better than that? But the last living moments of Carter in Halo: Reach are pretty awe inspiring as well.
Cortana and Chief in their final scene together in Halo 4. Throughout the entire campaign, I hated the way their relationship almost seemed amatory. Keep Cortana as the sarcastic companion please, not a sexy love interest. Just my opinion, I'm sure those of others are VERY different.
Every time I run through the Halo 3 campaign, I have to make sure that I save the marine in the beginning of the level FloodGate from being assimilated by the Flood. Be free, friend!