I don’t know about online, but if you have Comcast cable tv, Check out On Demand. In the "music" section, they have free guitar lessons. My boyfriend loves it!
References :

Hi , I´m a guitar teacher.
I think youtube is the best choice for free lessons. Just type the keywords that best describe your interest. For example: if you have an electric guitar, specify that on your search or ¨acoustic¨ if that´s the case.
In my personal opinion, learning from scattered unorganized free lessons is like riding in the dark. Consider having a teacher online. It´s not expensive and you go step by step following easy guidelines. When you register your e-mail in my website, you receive 4 free beginner videos. There´s also a link to download Tablature free software in the body of my home page. You´re welcome to visit.
References :
http://www.guitarsimple.com