LiveQuartz
Have you been looking for a free image editor with little to no luck? Look no further than LiveQuartz. It is a frontend on the various CoreImage functions that are available in Tiger, and that does mean 10.4 is required. The price is right, free that is, and the application itself has lots of features.
My one gripe with LiveQuartz? Metal, why does it use the Metal skin? The sooner Metal is gone from the OS the happier I will be. Otherwise this is a great little app that is already an universal binary (meaning it will run on PowerPC and Intel based Macs).