Our pal Geekosystem has gone into a lot of trouble ranking the 10 coolest planets of the Sci-Fi world. Listed at number 4 is the Mogo, a sentient planet:
Here's the list. See if you agree with the top pick: Link
We have Alan Moore to thank for Mogo, the sentient planet and member of the Green Lantern Corp. Frequently referred to as "he" despite lacking a gender, Mogo is one of the most solitary of the Lanterns, since, should he try to visit another planet, the force of his gravity might tear it apart. Mogo has complete control over his surface and weather patterns, which he uses to create the illusion of the Green Lantern emblem in green foliage, and he gladly serves as a training and recreation planet for the Lantern Corp. He also guides the trajectory of owner-less Lantern rings to new recruits. Over the span of DC continuity he has been host to a few transient races, though has never produced sentient life of his own.
Mogo doesn't like it when you compare him to a billiard ball.