I know you probably love a dozen tracks, please pick one, thank you in advance.
EDIT: Thank you all so far, especially everyone who kept it to one. I am at work currently and will make my way through the list but may not get a chance to thank you individually. I am checking them all out though and appreciating it.
Halo 2 OST - Impend
If you want the version with a little more oomph, there’s a remaster version. I listen to this for coding.