Here's an example. http://www.dtelepathy.com/ Look on the right side of the page (the plus sign). When you click it it comes out.
Anyone know what this would be called or where I can find a snippet somewhere?
Off-Canvas is the Word you're looking for. Foundation by Zurb has something like this included but also some of the links from campuscodi are very interesting. Especially the jpanelmenu got my attention.