Something that I have always loved in the classroom are short video clips.  Here are some links to some of my "go to" sources for videos clips in the science classroom:
National Geographic
Mythbusters
NOVA
Discovery
Ted Talks
Ted Ed
PBS Learning Media
WatchKnowLearn
Youtube Channels:
     Minute Physics
     Veritaseum
     Untamed Science
*Most of these videos will play commercials before them if you pull them straight from the internet. If you have iTunes you can subscribe to their respective podcasts and then you can download the podcasts you would like and they are free of commercials and spotty internet connection buffering :)