The Apple menu has a "Get Mac OS X Software" item which will take you to the Apple site. Look in the "Unix / Open source" section of the downloads and you'll find ImageMagick.
This is 11.3 Mb download, and it's an installer. You just double-click and run it. The only confusing thing is that it does not ask you where to install it, and it doesn't tell you where it put it! I had the installer on my desktop when I ran it and the files got installed in /usr/local/bin. The version was not quite as new as the sourceforge tarball, but I didn't have to build anything at all.

