We heard about anti-heroes yesterday, but Susan followed it up with a post about writing good villains:
Villains and antiheroes are cut from the same cloth--only villains give in to (or even revel in) their darker instincts, whereas antiheroes resist them. So delve into your villain’s history and try to root out the cause of their evil. Even if your villain is sympathetic, the reader should still recognize that he (or she) has beyond the pale--that he must be stopped no matter the cost.
She also adds ten reasons to love villains at the end of her article, so check it out here: http://www.omnivoracious.com/2011/10/sympathy-for-the-devil-how-to-write-killer-villains.html
Susan also adds a 'How to Write Mastermind Villains' interview with Richard Lee Byers:
Crossing paths with a mastermind villain is like being caught in a deadly chess game in which you can only see your own pieces. If you survive, it will feel like it’s just the mastermind toying with you. And despite working as hard as you can, what limited successes you achieve will feel like they are due only to the amusement of your opponent. Even in losing, a mastermind often achieves their esoteric goal.
You can find that article here: http://www.omnivoracious.com/2011/10/smarter-faster-meaner-richard-lee-byers-on-writing-mastermind-villains.html