I am trying to find a really simple way to create a key, or sort, which can be stored in a cookie that is used to log the person in when they have selected "Remember me", yet is impervious to a user who may happen to capture that cookie and try to use it for himself to gain access to the website... Any ideas?

I'm already using a secure session with "secure" cookies, but I'd like to take that a step further so that I'm not just checking to see if the value of the cookie matches the data stored in the database.