ClevelandWebDeveloper

Easily add tooltips to your wordpress site. Tooltips will show when target element is hovered over. On mobile devices tooltips show when target element is tapped. You can easily pick your tooltip color settings in Settings > Simple Tooltips.
<h4>How to Use</h4>
To define a tooltip (new, easy way): Click the tooltip icon on your visual content editor to add the tooltip shortcode. Change the content attribute to whatever you want to be the content inside the tooltip bubble. Change the tooltip trigger to whatever content you want to be used to trigger the tooltip, when hovered. (see screenshots)
To define a tooltip (old way): Add class “tooltips” to the target html element. The title attribute will be used for tooltip content.
<h4>Credits</h4>
Thanks to Stefan Gabos who made the original <a href="http://stefangabos.ro/jquery/zebra-tooltips/" rel="nofollow ugc">jQuery plugin</a>.

Simple Tooltips

I was seeking a tooltip plugin for images and this one makes it simple!  Others?  Not so much!  5 Stars all the way!  Thanks!

Easiest tooltip solution

Easily add tooltips to your wordpress site.

phonebook

This plugin inserts a TipMe icon in WordPress posts if the user has a Twitter username and has put the Twitter link in their website field of their profile. 
TipMe buttons for BBPress posts are inserted so users can get tips if they just have a 
Twitter link defined in the website field of their profile.
In short, it creates a tweet that the ChangeTip bot pics up and delivers with just one click.
We are using it on some of our web sites, so thought others might enjoy using it on theirs, but it comes without any warranty express or implied, and should be used at your own risk. It is a quite simple concept so should be quite reliable.
This probably will work with earlier versions of WordPress, but has not been tested.

TipMeWP

Inserts a "Tip Me" icon in WordPress & BBPress posts if user has a Twitter account & has put the Twitter link in website field

Simple Tooltips vs TipMeWP