This ones easy to answer, it's got to be Justin Guitar. Justin's a well respected session musician here in the U.K (he's actually an Aussie) and he's often called upon to give lessons to "stars" by their management (Kate Melua for example).
He has a huge library of lesson for free, and he works on a trust method which is highly regarded by Brian May, that is, contribute if you can afford it, if you can't, than don't.
http://www.justinguitar.com/
Ian.