GreatFFA is the free-for-all link system that generates it's page of links on the fly. Unlike rival scripts it doesn't simply write an HTML file, lagging your system. Instead, it uses a database and it's clever CGI to display the results dynamically. Everything is based on templates so YOU control the look and design of your site.
On command the listing page will also show sponsors of your choice. Unlike other FFA solutions, however, they are not static but are shown from an admin-defined pool of sponsors.
Configure the script to plug sponsors into the dynamically generated page every 5 links or every 10, whatever you like it's all up to you.
It have the option of compiling email lists to make sure that you can contact your users and keep in touch with them. Also included is an email template to mail users when they add a link if you choose.
As far as error and duplication checking is concerned, the script will do everything you want it to do and more-- no more mistakes steming from a bad database.