With 1888 videos and counting, VideoLectures.net seems to be an ideal collection of online video lectures. You must be warned that an amount of videos might be in foreign languages, and you will probably have to register to take advantage of certain features. Nevertheless you will hopefully find some lectures on subjects you are interested in.
For audible lectures Apple Education’s iTunes U has a great collection of university lectures etc.
Although both resources look good, I have really only listened to one lecture on iTunes, and you almost need textbooks or some other material to be able to follow.