The character database is currently still under construction. But you can now help filling it up with the information about your favorite (or least favorite ;) characters:
The Character Database Editor
I finally finished the first version of the "stephen-king.net Character Database Editor", which is a small application that will make it easy to enter character information into the live database.
More information and detailed steps on how to get and use the Editor can be found here.
The following stories already have a fairly complete or large number of characters entered in the database: (you can access any Stories character list by clicking on the "characters" link in the left sidebar of the story's page.)