When looking for the perfect software to create your own directory, there are a few things to consider. Since RSS feeds are so prevalent nowadays, why not find software that incorporates it? This would allow you to present the listings in a format that users could subscribe to. This also would allow you to add listings to your directory by importing an RSS feed into each category of your site.
A well written script would also allow you to import listings by having a Google and Open Directory importer. Perhaps the best software that I have found to do this is PowerSeek from http://focalmedia.net Just go to the category of your choice and import the matching category from Open Directory. For Google, do a search for the term that best fits your category of choice, and import only the listings that you find best suit that category.
When you run a directory, it would be nice to have the ability to provide premium listings in each category. This would mean having a second add url script where you can provide any additional fields that submitters can use to enhance their listing, and a link to a payment page that the submitter goes to after clicking the 'submit' button. The site administrator would accept the submission only after payment is confirmed.
Another good feature would be a spam filter that would allow you to block known spammer IP addresses, block domains or block specific email addresses. In addition, the add url script should also have a verification option to avoid automated submission scripts.
These are some of the things that I have found are helpful when looking for a good directory script. More later.