The quote "You're just jealous cuz I sound like a rock star" is a nod to Greg Cipes' actual career as a reggae-ska rock singer. On top of that, Cipes has lived on a vegan diet since age 8, and actually is a professional surfer, so he fits with Beast Boy's lingo.
Hynden Walch as the villainesses Madame Rouge and Blackfire.
Screwed by the Network: For unknown reasons, though various rumors have popped up, Cartoon Network chose not to renew the show for a sixth season. As a result, an episode that would have been great as a standalone piece becomes underutilized as the series finale.
Vocal Evolution: Greg Cipes's voice broke halfway through season 1, forcing him to using a higher voice which became his trademark.
Raven's voice also sounds considerably different in early episodes. It was more high pitched and nasal. I guess puberty struck both of them.
What Could Have Been: In the comics, Brother Blood is the title of the leader of the Church of Blood. The Church of Blood is a cult that worships Trigon, and the leader is specifically the emissary of Trigon himself. How cool of a tie-in to season 4 could that have made?
Blackfire completely disappears after Betrothed, even though she would be eager to get revenge on Starfire for overthrowing her rule of Tamaran, and thus would have probably wanted to join the Brotherhood of Evil...
Blackfire actually does appear again, in an issue of the comic series, where she teams up with Madame Rouge while still in jail. In that issue, Starfire's backstory is revealed and Madame Rouge poses as the girls' brother, Wildfire. Starfire sees this as a Moral Event Horizon, and finishes the issue with a vow to find Wildfire. Nothing is ever said about it again.
The series was not supposed to end at season 5; the final episode, Things Change, was supposed to plant the seeds for a sixth season, which never came to be.
Beast Boy's design was originally very different. Wondergirl was meant to be a part of the Titans, however she wasn't put it due to legal reasons.
Slade was supposed to team up with the Brotherhood of Evil in season 5 and become a (successful) Starscream. Instead, he gets relegated to a cameo in the final episode.