If you want a flexible directory platform then http://www.wsndirectory.com/ is worth a look. It's a got a huge amount of features, custom fields, member management, full templating system, can bind entries to (included) postcode data, ecommerce options for paid listings/ads/sponsorship, maps integration and even multilingual. No 3rd party addons needed to build something really powerful.
If you want something a bit lighter then http://www.esyndicat.com/ might fit the bill. Out of the box it's a basic directory system with your usual stuff like custom fields, member management, but you can extend it with their plugins.