Nokogiri (v1.5.0, specifically):
Mostly follow instructions from here. libxml2, libiconv, and libxslt library versions will probably be different, but to install with those libraries in general, run:
gem install nokogiri -v '1.5.0' -- --with-xml2-include=/usr/local/Cellar/libxml2/2.9.1/include/libxml2 --with-xml2-lib=/usr/local/Cellar/libxml2/2.9.1/lib --with-xslt-dir=/usr/local/Cellar/libxslt/1.1.28 --with-iconv-include=/usr/local/Cellar/libiconv/1.14/include --with-iconv-lib=/usr/local/Cellar/libiconv/1.14/lib