The villains for the previously mentioned Top 50 list are below. I have room for six more and I'm listening for your suggestions.
But please don't waste your breath and my time on the shallow, ridiculous caricature that is "Darkseid". No matter how large you make a cardboard cut-out, it's still basically two-dimensional....
The Joker. The clown from hell.
Two-Face (Harvey Dent) . All of axiology wrapped up in one character.
Lex Luthor. Human ambition, vanity, and folly all in one package.
Mxyzptlk. He who uses the fourth wall to look IN at the comic book, as we do, instead of out.
The Riddler (Edward Nigma). The supreme intellectual challenger.
Dr. Psycho. He violates you from the inside out.
The Composite Superman (Joe Meach). The godlike janitor who kicked Batman and Superman's butts.
Starro. If you do not immediately understand the genius of a giant purple mindcontrolling starfish from outer space that eats atomic power, then may god have mercy on your soul.
Eclipso (Bruce Gordon). No one else is his own archenemy.
Gorilla Grodd. It's the juxtaposition of the gorillaness with the mindforce/scifi thing, ya see.
Penguin (Oswald Chesterfield Cobblepot). There is no rationale to fully explain the fabulousness of the Penguin. Yet there it is. Besides, what other villain can fight Firestorm to a standstill in one comic and get beaten up by Bullock in another without your batting an eye about it?
Catwoman (Selina Kyle). The real danger to society isn't evil; it's disinterested amorality, as symbolized by Catwoman.
Emerald Empress. The eye. THE EYE! AAAIIEEEEEEEEE!!!!!!!!!!!!!!!!!!!!!!!!
Mister Mind. A world-conquering worm. Sheer genius.
Harley Quin. Because I, too, have had bad days and made bad decisions.
Killer Moth. The original Anti-Batman, the unlovable loser, and the avatar of all self-deluding costumed kooks.
The Crime Doctor. It's like "snakes on a plane".
Black Manta. Because ... well, because he's Black Manta, for Neptune's sake.
Ares (God of Conflict). A real god. Not a thundering Norse puppet character or a cardboard-thin fourth world "new god" or a wispy Endless One. A real god from the gods the founders of our civilization worshipped.
Paul Gambi. Tailor to the supervillains. Pure poetry, that.