I already can get the content of an Iframe with jQuery, though I would like to learn how to get it with pure JavaScript.
This is what I have so far.
If it is on the same domain, try this. It won't let you access iframe contents if the iframe is of a different origin than the window that you are viewing.
var iframe = document.getElementById("awc_frame");
var iframe_contents = iframe.contentDocument.body.innerHTML;
Working example with jsfiddle iframe viewing a page on the same domain:
http://jsfiddle.net/tqAL3/1/