A couple of weeks ago I did my Top 10 DC Heroes. Today, I’m doing my Top 10 DC Villains.
10. Brainiac
9. Mirror Master
8. Sinestro
7. Ra’s Al Ghul
6. Zoom
5. Two-Face
4. Deathstroke
3. Darkseid
2. Lex Luthor
1. The Joker
Honorable Mentions: Bane, Doomsday, Black Manta, Captain Cold, Black Mask
Did I forget anyone?
I guess you're looking for individual villains, so the Secret Society of Super Villains won't count. From that group I'd throw in the Wizard and maybe Gorilla Grodd.
I'd suggest Deimons from The Warlord; Vandal Savage, Psycho Pirate, and Per Degaton from JSA/All Star Squadron; Despero and Kanjar Ro from the original JLA. And I always liked Emerald Empress from the Legion of Superehroes.
As you can tell, I cut my teeth on comics in the 70s and early 80s.
Grodd is another good one.
Vandal Savage (who I compltely forgot about) at least deserves an honorable mention. My favorite appearance of his is in the DC One Million graphic novel.