Well, there is PixelNhance, ToyViewer, and GraphicConverter (not free). I have Photoshop and still use PixelNhance and ToyViewer for many things. The interface in PixelNhance is way easier than Photoshop for the same processes.
I also use Create (from Stone Design, also not free and is more for illustration and layout) for some things... mainly text as Cocoa apps work better with fonts than Carbon apps (even Adobe's apps).
There is also TIFFany3, which is no longer supported. It is about the same price as Photoshop Elements. The developers are working for Apple now on CoreImage, so much of the TIFFany3's functionality should be available to all developers with the release of 10.4.