In psychiatry we have nine defined personality disorders. These represent a stable set of behavioral patterns that are consistent across multiple environments and over time. Briefly, they are:
Paranoid: They may not be convinced the FBI is spying on their every move, but they aren’t ruling it out either. Basically they see the world as a dangerous, aggressive place.
Schizoid: The content loner, off on their own but happy to be so, generally pursuing solitary activities, especially collections of various sorts.
Schizotypal: Eccentric right up to the point of being psychotically delusional but not quite. They have magical beliefs and tend to come across as rather odd.
Antisocial: No, they don’t avoid parties. They have a disregard for rules, societal norms, and how you feel about what they’re doing. They tend to be career criminals.
Borderline: Not easy to deal with. They are prone to emotional outbursts, tend to see the world in absolutes, fear abandonment above all else, and can go a little psychotic when stressed.
Histrionic: Dramatic and generally provocative. They’re entertaining to have around, but I wouldn’t be alone with one if I were you…unless you’re single and feeling daring.
Narcissistic: Yes, they think they’re all that, and they’re dangerous if shown to be otherwise.
Avoidant: They also wind up as loners, but it has more to do with a fear of scrutiny and public embarrassment.
Dependent: They can’t make a decision and would really like you to make it for them.
Obsessive Compulsive: No, they don’t wash their hands 100 times a day. This group is the epitome of anal retentive, liking things to be in order, parallel, perfectly right. They don’t delegate well and can be overly concerned with right and wrong.
The fun part of knowing these diagnoses (http://psyweb.com/Mdisord/jsp/mental.jsp for full criteria) is that you can diagnose your friends and family. Also, these represent stable, realistic, and common archetypes of human behavior upon which to base characters. You don’t have to make someone exactly fit a diagnosis, cause real people rarely fit exactly either, And you don’t have to keep a character in that role for a whole story (remember the whole dynamic vs static character thing from Eng lit). Deciding on a character’s makeup and underlying psychology will help you keep them consistent, cause nothing kills a story more than plot-convenient behavior that defies a character’s previously described idiom. It also helps the story to feel real when what goes on manages to ring true or remind the reader of things they’ve noticed in real life.