In terms of size
Galactus, in his base form is bigger than the Earth. Probably about Jupiter or Saturn sized.
Should probably also mention Galacta, daughter of the above (yes really).
Ego the Living Planet is, well, planet sized.
Mogo, a living planet from DC.
Anti-Monitor is huge, though not sure how big exactly.
At one point, Mikaboshi was as big as a planet.
God Swamp Thing was bigger than the Earth.
The Infinites - They make Eternity look small.
Apocalypse Beast - Is nearly 16, 000 feet in height. Also has a mouth with teeth and eyes on its tongue in its mouth. As opposed to the mouth on its chest.
Adjudicator - Makes Galactus look small.
Exitar the Exterminator - Usually referred to as the largest Celestial.
Living Tribunal - Has no neck but can still wear necklaces.