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.
GSInnerZoom is a jQuery plugin that permit you to do an inner zoom or magnifier inside an image.
Cloud Zoom is a free jQuery image zoom plugin, a comparable alternative to products such as Magic Zoom. Compared to the popular jQZoom plugin, Cloud Zoom is smaller, has more features and more robust compatability across browsers.