I stumbled across another interesting (and free) image manipulator in Apple's downloads section by the name of ImagePlay. It's actually an open source editor with versions available from Sourceforge for OS X, OS 9 and even Windows, but because of that open-sourceness it doesn't appear to be utilizing all the abilities of CoreImage like ImageTricks does (correct me if I'm wrong). However, ImagePlay does offer a few key features, such as layers, various effects and filters, as well as the incredibly handy ability to offer an estimated file size when exporting various image formats such as JPEG, PNG, BMP (uh, why?), Photoshop, TIFF and even QuickTime.
While it obviously isn't Photoshop, I'm sure ImagePlay can still find its place in plenty of people's Application folders. This handy little image editor is available at either Apple's Downloads section or from its home at Sourceforge for the amazingly low price of $0.