phpLD : phpLD is the most widely used directory script on the internet.
phpLD

phpLD Screenshot
Overview
phpLD is the most widely used directory script on the internet. Users have tested the script on over 50,000 websites, and its a script that works in nearly all PHP hosting environments. Another great advantage of phpLD is the number of templates and mods available. There are complete sites devoted to mods and templates.

Visit Site

Features

Paypal Integration for Selling Featured Links
Set Expiration for Featured Links (ex. sell monthly, annually, lifetime)
Validation
Emailer
Create Reports of Link Request Emails sent to show your customer
Notify Submitter of Link Submission Receipt
Unlimited Categories and Subcategories (tested on 2 million+)
And much more!