I am really entusiast to suggest you a good Syntax Highlighter for Joomla.
Download the package from "Code is ?" website.
Before install the plugin in Joomla you need tu unzip the package. You will find the plugin and the button for editor TinyMCE. Install the hightligher plugin and then the button.
note: that the button is installed in the footer of the edtor and the label is "Insert Code". Do not fall in the mitstake to search the icon in the header.