Would you like to Make a ‘View Source’ Button on your website? Click it, and you see the entire source code for the page you are looking at. It’s not a popup or a new tab, it just shows the source right there on the page. It works on pretty much all modern browsers, as long as it supports CSS3 :target. Breaks in IE 8 and down, but OK in IE 9.

Requirements: jQuery Framework
Demo: http://css-tricks.com/examples/ViewSourceButton/
License: Apache License