ImageMagick v6.0 has been released, and includes one particularly useful addition: combining up to three grayscale images into a single RGB image (one grayscale image per channel), which is something I will use often. The ImageMagick package compiles from source on OS X (though I suspect Marc Liyanage might well put a package together soon), providing a load of command line tools for manipulating, resizing and converting images, while PerlMagick provides access to the toolset from within Perl scripts.