http://webcast.berkeley.edu/index.php [3]
This website has really good lectures for chem, bio, physics, psych (really good psych), etc. For the chem and physics, lectures will help with concepts, but practicing is vital. About the website, it has webcasts and podcasts and could be downloaded for mp3.
Hope it helps.
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"Music is the movement of sound to reach the soul for the education of its virtue."
-Plato