All of them encapsulate the particular sound that was produced in the 2000's.
Princess Diaries franchise:
Miracles Happen is good but the version in Spanish (Siempre Hay Milagros) is supreme.
Let's Bounce (from the scene in the second movie where they're sliding down in mattresses).
Breakaway .
Confessions of a Teenage Drama Queen:
Drama Queen (That Girl)
Freaky Friday:
Take Me Away (and generally anything Lindsay Lohan, like the song Rumors or First).
Legally Blonde:
Perfect Day (I find Hoku to be spiritually adjacent to Natasha Bedingfield, idk why). Thanks to the intro of Legally Blonde, I ended up discovering another song by Hoku that ironically isn't in this movie, but some other movie: Another Dumb Blonde .
From Olsen Movies:
Us Against The World-Play.
Hey Baby-No Doubt.
My only exception to this rule is Zoey 101 with their theme song and the soundtrack from H2O, especially the song No Ordinary Girl.