Mudbug Software has just released a beta of their image editor "Webify". Webify is small, lightweight, and powerful at the same time. Webify is meant to be used to help you prep your images for the web.
One of the cool features of Webify is that there will be an SDK that will be made available when the final version is released. An SDK will allow other developers to create "add-on's" or "plug-ins" that will extend the functionality of the application.
Webify uses the core graphics that are built into Leopard so the changes that are made to images are super fast.
There are several plug-ins that come pre-installed with the beta with the promise of a couple of more to be added to the final version which should be available in October.
If you want to see some screenshots of Webify then be sure to drop by the Mudbug Software website and read up on Webify.