Khanacademy is excellent since it has a tree diagramm of subjects on which you can see how far you have come and what material you need to learn in order to understand the topics. The big problem with LessWrong's sequences is that they are highly entangled in contrast to the highly hierarchic way people usually learn. The other problem is that the useful or better articles came later in the sequences so that one has to read older, less interesting ones in order to understand the vocabulary of the newer articles. Maybe the sequences should be rewritten with this in mind?