Here are two open source libraries that I wrote (and use all the time). I discuss them in depth in one chapter of ActionScript 3.0 Image Effects.
aeon animation — A simple animation library for interpolating values and creating nested sequenced and composite animations. Works with filters and 3D transformations as well.
aether effects — A library on which to build complex image manipulation effects using nested simpler effects that can be overlaid with blend modes and opacity.