I had a very very tough time trying to find the solution to this.  So, I am compelled to post what solved my problem.

First off, when you go looking for solutions in Stackoverflow, etc., do look at the dates when the problem and the solution was posted.  Usually, the closest dated solution will be your best candidate.

So, here's your checklist of items:

  1. Install XCode 4.5.2 (get it from App Store).

  2. Open XCode > Preferences > Downloads > Components.  Install Command Line Tools.

  3. Install XQuartz.

  4. Install Imagemagick via brew but not using the bottled build.

brew update
brew install imagemagick --disable-openmp --build-from-source
  1. Link the necessary libraries.
$ cd /usr/local/Cellar/imagemagick/6.8.0-10/lib
$ ln -s libMagick++-Q16.7.dylib libMagick++.dylib
$ ln -s libMagickCore-Q16.7.dylib libMagickCore.dylib
$ ln -s libMagickWand-Q16.7.dylib libMagickWand.dylib
sudo ln -s /usr/bin/gcc /usr/bin/gcc-4.2
  1. Finally, install Rmagick.
$ gem install rmagick

Whew. Took me almost 8 hours in total to figure this out. I hope this saves someone else's hours! :)