A few great ones that come to mind (in order of personal preference, decreasing)...
117 - from Halo 4 broadsword mission
Impend (or the remastered version
Impart) - from various Halo 2 missions
Never Forget - Halo 3 title screen
Peril (or the remastered version
Jeopardy) - from various Halo 2 missions
One Final Effort - Halo 3, warthog run in final mission, and elsewhere
Tip of the Spear - from Halo Reach mission "Tip of the Spear"
Finale - from Halo 3 ODST
Tribute - from an ending cutscene in Halo 3
Epilogue (0 - 0:52) - from Halo Reach ending. "There will be another time..."