You could hide some contents in posts, then those who have not replied to any posts will not see them.
Quickly add tables to any post or page using simple shortcode tags.
Adds a tree of all your pages or custom posts. Use drag & drop to reorder your pages, and edit, view, add, and search your pages.
Quick contact box is a nice widget that shows phone numbers, address and email
jQuery plugin to create google maps with advanced features (overlays, clusters, callbacks, events…)
Keep your PHP and WordPress seperate, using the shortcode [php-to-page] you can include PHP files in your pages.
Allows the use of iframes in your blog using a custom shortcode