MaGiKS Proper PHP Include lets you easily, quickly, efficiently and safely insert PHP code into posts, pages and/or widgets, without disabling the Visual Editor. You simply upload a php file containing your code into your theme folder and use a WordPress shortcode to “include” that file into your posts/pages/widgets.
Debug Bar adds a debug menu to the admin bar that shows query, cache, and other helpful debugging information. A must for developers! (requires WordPress 3.1)
WP Mobile Detector automatically detects if the visitor is using a standard mobile phone or a smart phone and loads a compatible WordPress mobile theme for each.