Easy Footnotes lets you quickly and easily add footnotes throughout your WordPress posts using a simple shortcode in the text editor.
Add hover text (aka tooltips) to content in posts. Handy for providing explanations of names, terms, phrases, abbreviations, and acronyms.
Magic Tooltips For Contact Form 7 is a WordPress Contact Form 7 tooltip plugin that let's you add tooltips to the Contact Form 7 form fields.
WordPress tooltip lets you add tooltips to content on your posts and pages.
Add tooltips from "WoWHead" (http://www.wowhead.com/), useful for blogs etc. about World of Warcraft.