Good long presentation:
http://www.youtube.com/watch?v=OC1OixM_118

Comedy presentation:

How Not to use PowerPoint
http://www.youtube.com/watch?v=lpvgfmEU2Ck

Some short points:
http://www.youtube.com/watch?v=itjSaEYDOgY

http://www.youtube.com/watch?v=eUlzZbFewzY

http://www.youtube.com/watch?v=2XFexzhDHxQ

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