Yertle is my favorite of Dr. Seuss's books because it's more lesson than nonsense. That's my personal preference - you might not agree. But the rhymes, characters and illustrations are as fun as you could ask for.
There's Yertle, who tries to improve his own situation by stepping on other people, and learns a lesson. There's Gertrude McFuzz, who wants a fancier tail just like that other girl, and learns a lesson. And in the last story, there are a set of animal characters who try to out-boast each other... and learn a lesson.
My kids are always asking for "the Yertle book." It's classic Seuss, and a full five stars.
Yertle the Turtle is the story of Yertle who ruled a happy clean land until his power went to his head. Then he was mean to his subjects and causes them problems. This book is good to discuss how to treat others with younger kids.