I used a script to install ImageMagick http://github.com/masterkain/ImageMagick-sl
After a while, I got ImageMagick installed.
Then I ran sudo gem install rm
For those who got
InitializeMagick() in -lMagickCore... no; -lMagick... no; -lMagick++... no;
this worked for me in OS X 10.8: https://github.com/maddox/magick-installer
From here: RVM + Ruby 1.9.2 + Rmagick + Lion = System Works, RVM Doesn't