I don't know if this has been posted before but people surely need reminding about this fantastic teaching resource.
Chess.fm has published a series of free online videos by grandmasters and international masters. Each one is 20 or 30 minutes long. Check them out here:
http://www.chessclub.com/chessfm/videos/
Some are a bit dry and/or patronising but some are spot on. My personal favourites are all the ones by GM Varuzhan Akobian.
Enjoy!