Just off the top: Krusty the Clown, Groundskeeper Willie, Luigi Risotto, Fat Tony and his crew, Bumblebee Man, Cletus (if we're counting slackjawed yokel as an ethnicity), etc.

Many of the characters are broad, cartoonish stereotypes by design.

Yes, Apu is more prominent than most, but part of it is bigger he's had a bigger role than most of the secondary characters.