As the number of Wordpress users increases and the needs of users change, Premium plugins are a good option if the plugin performs an essential role in enhancing your site. The outlay in money for the plugin (if the plugin is good) will usually pay itself back fairly quickly. Personally, I have only purchased Autoblogged, and that plugin has been great for me and is an absolute steal for what it does. With the advent of Premium themes, people have started using Wordpress for more than just blogging and sites which are more involved with a lot of specific content on a particular topic/theme or product. A list of premium plugins I’ve found are listed below.
I would be interested to get some feedback from anyone who has used these plugins.
Plugin name: OIO Publisher
Function: Manage all your advertising from the admin panel in Wordpress
Price: $47
2. WP-REVIEW SITE
Plugin name: WP Review Site
Function: Turn Wordpress into a powerful review site engine
Price: $97 (normally $199.95)
Plugin name: Wordpress on Crack
Function: Easily write WordPress plugins in PHP
Price: $97
4. VIVA THUMBS 
Plugin name: Viva Thumbs
Function: Easily add thumbnails on the fly
Price: $14.95 (single), $49.95 (multi-site license)
Plugin name: Autoblogged
Function: Easily automate your blog posts by configuring intelligent RSS and blog searches
Price: $59.95 (single license), $129.95 (unlimited sites)