spzoom is a jQuery plugin to create simple hover image zoom. There are some options to custiomize width, height, position, margin of the zoom display area.
jfMagnify is a jQuery plugin that creates a magnify glass effect. This plugin will magnify html content, not just images.
Zoomify is a jQuery plugin for simple lightboxes with zoom effect.
MagnifierRentgen is a simple, lightweight, responsive magnifier hover plugin. (magnifying glass effect)
Zoomerang.js is a drop-in library that allows your users to zoom in on (almost) any element on your existing page. It works even if you resize or scroll your page.
SergeLand Image Zoomer is free jQuery image zoom plugin the magnifying glass effect.
Panzoom is a progressive plugin to create panning and zooming functionality for an element.
Rather than setting width and height on an image tag, Panzoom uses CSS transforms and matrix functions to take advantage of hardware/GPU acceleration in the browser, which means the element can beanything: an image, a video, an iframe, a canvas, text, whatever.
Additionally, every article on the interface will have a zoom on mouse hover effect. This zoom effect can be toggled at run time by pressing "b".
elevateZoom is a free Image zoom plugin with options for window zoom, inner zoom, lens zoom. Tinting and easing can be enables. It is distributed under GPL and MIT license.