See also ImageOptim
ImageAlpha is a GUI for pngnq and pngquant. It allows you to easily generate paletted PNG images with full alpha channel and test how it will look against different backgrounds.
Requires Mac OS X 10.6.1 (Snow Leopard).
It's open source (Python + Cocoa). Please have a look at the code and see if you can improve it! The application is still in early stage of development.
