You have a small area. You mouse over it. An area pops up giving you a zoomed in closer look. AnythingZoomer is a jQuery plugin that does it.
It’s flexible in many ways, in that the “small”, “large”, and “zoom” areas are all pretty easy to customize via CSS. It’s inflexible in other ways, in that it doesn’t “automatically” work by cloning content or anything like that (which is arguably more flexible), and the HTML structure is fairly rigid.
Requirements: jQuery Framework
License: License Free