'Zoomer' is a JavaScript component authored by James Padolsey, and is currently for sale on ThemeForest.net.
To use this demo simply hover over the image below; you can use your mouse-wheel to zoom in/out (Note: Just for this demo, this feature is not enabled in IE).
No images are used in the plugin itself. The "zoomer" box that appears when you hover is generated dynamically. Whoever uses this plugin is able to specify the size, the shadow levels, and the radial-gradient intensity, as well as the min/max/default zoom levels.
The documentation you receive with the purchased component includes a detailed overview of the jQuery plugin, two screencasts (videos) and an FAQ!
*** If this demo doesn't work straight away please wait a sec while the photos load.
Almost every aspect of the zoomer is customisable. Here's an example showing a zoomer overlaying a grayscaled photo; the zoomer itself has custom dimensions, a slight red-tinge and no shadow:
To buy this component please visit ThemeForest.net and navigate to the "components" category.