Hunting for the best user authentication class

[sKunKbad]

I have a fairly basic user authentication class that I am working with, but it doesn't do everything I want it to do. It uses a MySQL database for users/passwords. Passwords are encrypted. The session is regenerated for every page. I've been researching security issues and  trying to make sure my class is as secure as possible. I want to make sure only one person can be logged in to an account at a time, and have a good idea of how to do it, but I'd like to see some other really good user authentication classes that people are using. Most of the ones I have seen online are too basic and lack any security, and I'm wondering if anyone can point me to a script or two to check out. I know about the PEAR AUTH package, but I'm looking for non-PEAR classes only.

 

Thank you.