The Official WordPress Directory lists thousands of fantastic plugins which optimise WordPress and enhance it’s functionality. Some developers update their plugins regularly, either to add more features or to make sure their plugin is compatible with the latest version of WordPress. Understandably, many developers just don’t have the time to update their plugins or devote all their time to it due to other commitments (work, family, other projects etc).
Premium WordPress plugins are usually better supported as the developers are getting paid for their work. In general, this allows plugins to be more in depth and add more functionality to WordPress. In this page you will find a list of marketplaces where you can purchase premium plugins. I encourage you to check out my list of WordPress plugin shops as well.
CodeCanyon is by far the largest marketplace for premium WordPress plugins. Thousands of WordPress plugins are available for sale.
These plugins differ in quality, from advanced plugins that add a lot of functionality to small solutions that are available for just a few dollars. Be sure to check the comments area for every plugin to get an idea how good support is for the product.
Formerly known as Mojo Themes, Mojo Marketplace is a web development marketplace that sells WordPress themes, Joomla themes, eCommerce themes, and other types of website templates. They are primilarly know for selling designs, but they also have a good selection of premium WordPress plugins.