http://www.entropy.ch/software/macosx/#imagemagick
or this
http://mac.softpedia.com/get/DTP-Prepress/ImageMagick.shtml
:edit:
Actually I think they are just imagemagick itself, does Mac o/s not have a way of installing software through a software package repository, in ubuntu we have synaptic, and it automatically check dependencies and installs them. I'm sure Mac o/s must have something similar.