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.
Hover-Zoom jQuery plugin
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.
Also Picbox WordPress plugin is now available.