Cambridge Nights is the best source of interviews of scientists intended for a general audience that I've seen online. Each interview is about 45 minutes long, which is just long enough to explore each scientists' work. The host is a scientist himself, César A. Hidalgo. He does a fantastic job of selecting interesting guests, asking probing questions that cover the important bits of the scientists' work and keeping the discussion at a high level that is interesting to the viewer. Hidalgo also examines the scientists themselves--their upbringing and career progression, which is fascinating and useful for kids who might be aspiring scientists.

So far, my favorite interviews are with Lant Pritchett (international development, education) http://cambridgenights.media.mit.edu/index.php/2011/lant-pritchett

And also with Juan Perez Mercader (astrobiology) http://cambridgenights.media.mit.edu/index.php/2011/juan-perez-mercader