Johnson on ODST's firefight while throwing a nade.
"Only a man can do this!"
If you want my favorite serious line, it is the gravemind in Halo 2 and 3. These lines, I can't choose between.
"There is still time to stop the key from turning, but first it must be found."
"This is not your grave, but you are welcome in it."
"We exist together now, two corpses in one grave."
"Silence fills the empty grave, now that I have gone. But my mind is not at rest, for questions linger on. I will ask, and you will answer.
"Do not be afraid. I am peace; I am salvation."
"Now the gate has been unlatched, headstones pushed aside; corpses shift and offer room, a fate you must abide!"
"Child of my enemy, why have you come? I offer no forgiveness, a father's sins, passed to his son."
I guess I should stop now, I have too many to put here...