New SMART Plugins project for jQuery & CSS is Smart Image Tooltip. This is easy to setup and use plugin to show image based tooltips for links and thumbnails or any other HTML element with correct markup.
Tooltip is displayed using predefined (or custom) templates, allowing to incorporate additional data beside the image. It has click and touch control for opening the tooltip and detects mobile devices. There are many jQuery plugin options to customize tooltips and you can see it in action on demo page.