I tried to install Nokogiri on my Ubuntu 12.04 system, and got an error that said \"libxslt is missing\", but the libxslt-dev and libxml2-dev
I was having this issue on Ubuntu 13.04.
I had tried everything that you find all over the place online. Making sure packages listed on the Nokogiri install page are present, etc etc.
The only thing that eventually did it for me was installing libsxlt from source. After that everything worked perfectly.