For me, it’s gotta be from Road To Perdition… the one just at the closing credits where the kid (Tyler something or other - he plays Michael Sullivan Jr.) has his last few lines of the film.
To me it just emotes a sense of classic-ness that time forgets. It’s absorbing and drowning at the same time.
And it has this wierd effect of being extremely sad yet sort of positively uplifting too.
I was going to suggest “You’ve Got a Friend In Me” from Toy Story (especially the version sung by Robert Goulet), but that was pre-2000.
So I’ll continue the Pixar trend and go with the “Scare Floor” theme from Monsters Inc. – very reminescent of “Powerhouse,” but not a derivative of it, and imminently hummable IMO. Power horns!