World Wide Ad Maker
This script allows you to register users who can create ads with pictures, description, and keywords. You can set up a default picture for those ads with no picture. It has a search page with allows users to search by category. You configure the categories in an easy array. You can use it as a classifieds, personal ads, penpals, etc. It allows users to mail back and forth without revealing email addresses. You can also configure the background and text colors.