Though it's a bit older of a tutorial, with the new redesign of Evolt more people have taken notice (on del.icio.us especially) of this tutorial on their site - "PHP Login System with Admin Features".

I wrote the popular evolt.org tutorial PHP Login Script with Remember Me Feature mainly as an introduction to user sessions and cookies in PHP. Since it was created as a learning tool, many advanced features were left out of the script. By popular demand, I have written and am presenting here a complete Login System, with all the features that were left out of the first script, that can be easily integrated into any website.

This article is intended primarily for intermediate to advanced users of PHP, as it is not exactly a tutorial, but a description of the implementation of an advanced Login System. Beginners who are looking to learn about user session and cookies in PHP are advised to read the above mentioned tutorial before reading this article.

He includes lots of features in the system, including: better security, member levels, an admin center, visitor tracking, forgotten password help, and much more. The entire code for the application is laid out so there shouldn't be a problem with getting it all set up - of course, he also doesn't give much in the way of explaination of the code, and instead leaves that to comments...