Added AnimationToPNG utility script to output a series of PNG files from an animation.  Output includes alpha for transparency, works with Unity Free and Unity Pro.  Uses Render Textures for full camera resolution and can only be used with Unity Pro, without Render Texture, the screen width is split between 2 cameras, black and white, and the alpha is created from the differences between the images rendered from the 2 cameras.

The AnimationToPNG prefab includes the cameras and the script to export animations to PNG files.  Just drag the prefab into an empty scene along with the animation to be exported, and press "Play".