CamanJS
"The main focus of CamanJS is manipulating images using the HTML5 canvas and Javascript. It's a combination of a simple-to-use interface with advanced and efficient image/canvas editing techniques. It is also completely library independent and can be safely used next to jQuery, YUI, Scriptaculous, MooTools, etc. CamanJS is very easy to extend with new filters and plugins, and it comes with a wide array of image editing functionality, which is only growing as the community makes more plugins. "