I find Extra Credits simplistic, it's useful mostly to new designers. Videos made by actual game designers are far more useful in my humble opinion.
Chris Crawford
https://plus.google.com/u/0/105363132599081141035/posts/2c8nSivyukS
Sid Meyer
John Cleese from Monty Paython (not a game designer, but his talk about creativity is more than related)

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