The you should look no further than to these scripts:

• PHPLinks: http://sourceforge.net/projects/phplinks/
• Site SIFT: http://scripts.site-sift.com/features.php
• Arfooo: http://script.arfooo.net/features/
• PHPWeby: http://phpweby.com/features/dir

Currently my favorites is Artfoo and PHPLinks since they bouth seem to be great open source search / link directory’s which also include some handling of Ads (e.g. Google Adsense.)

All of the above open source link directory’s require PHP/MySQL..