As in characters who are basically pure evil and have no real redeeming qualities whatsoever. Yes, I know it's not realistic (at least most of the time). But sometimes, I want a cheesy bad guy.

A perfect example would be the Dark Lord Sauron. There aren't really any shades of grey to this character. He is pretty hard to add shades of grey to a character who wants to bend all life to his will.

I really love this classic video of comparing Sauron and Voldemort.