I feel your pain.
The problem is that if you install ImageMagick and ImageMagick-devel from yum you end up with version 6.2.x instead of the required 6.3.x or higher that RMagick requires.
Just install from source. Follow these steps.
wget ftp://ftp.imagemagick.org/pub/ImageMagick/ImageMagick.tar.gz
cd ImageMagick-6-??
./configure
make
make install
gem install rmagick
Relax with a beer.
