Flyleaf - Cassie (Simlish) The Sims 2: Teen Style Stuff
This is a bit of a deviant upload and more focused on a song I couldn't find in HQ.
After a bit of digging and extracting packages from TS2:TSS, I finally found a higher quality version of Flyleaf's - Cassie among other songs that are unnormalized through YouTube uploads. To my knowledge, no one has uploaded an HQ version of this song, nor a full version of a somewhat high quality in-game music of this, so here's a more clear version of the song. Despite it being rendered to 128kbps and formatted to mp3, you can really hear the difference between what's available on YouTube and this version.