JR qTip for WordPress is a plugin that uses qTip to display nice looking, user friendly tooltips. Colors and position are easily changeable.
Use QR Codes (Google API or QR Code Lib) anywhere in your blog, as a Widget, Shortcode, Tooltip or with a PHP function.
Popupper is a plugin that enables a blogger to add popups of images and text into their posts.
"Youtube ToolTip" Click on any of your links to get a quick preview of the youtube video.
All-in-one-Qype-Suite "Qypifys" your Blog! Add tooltip-links to Qype Places, geotag Post & pimp sidebar with 3 nice Qype Widgets
This plugin allows you to easily insert buzzwords with unical alt-title into your blog.