Khan academy is nice for the material it covers, but anybody going beyond high school will find it rapidly becomes obsolete (according to the content ca. the last time I checked). The treatments are simply too elementary and the topics too low level.
I would think a site where people can ask anything, ala stackoverflow, would yield more useful results for many physics/math/cs students.
I would think a site where people can ask anything, ala stackoverflow, would yield more useful results for many physics/math/cs students.