This will sound like a homework question, but it’s been 20something years since I was in high school so you’ll have to trust me that it’s not :).
It’s easy to find ways in which Shakespeare’s villains feel guilt for their actions, whether it’s Lady Macbeth’s sleepwalking, or Claudius’ outright “My offense is rank, it smells to heaven” prayer. Should we count Edmund’s last minute redemption, too?
What I’m interested in is bad guys who feel no guilt at all. I was trying to explain to my boss last week why Iago is such a nasty son-of-a-gun, and I realized that when it comes to his actual crimes, there are other bad guys that did far worse. It’s just something about him. I think it has a great deal to do with the fact that, as far as I can tell, he never feels a shred of anything for his victim, right up until the last words we hear. That’s what’s so scary.
Who else? I’m expecting Richard III to make an appearance, though truthfully I’m not familiar enough with the play to know if he has any moments where he stops to think about other people.