Here are two Youtube science channels I think are really cool:
Minute Physics - http://www.youtube.com/user/minutephysics
Really cool summaries on some of the stuff we see happening in Astro and Particle physics (usually), right up my alley were interests go. Occasionally covers fun non-science (as opposed to "nonsense") stuff.
Here's one of my favorite:
Smarter Every Day - http://www.youtube.com/user/destinws2
First caught my attention today because it involved cats! (yay!!!) Covers a wide range of topics and I really enjoy his presentation style. As I've commented on my Facebook page - Move Aside, Savage!!! heh.
And here's the one with the kittehs! :)