"The Future Channel: Connecting Learning to the Real World" has some great math and science videos with teaching activities. Check out the Hands-On Math section of their website for a list of math activities by topic. Go to a category and click on "Get the Activity" for the topic you want to see. At the bottom of each activity you will see a video that relates to the concept taught in the activity (it is sometimes related to the activity also, but not always).
You may also go to The Complete Movie List and choose a movie to view. Each movie page has links and descriptions for all related activities under the video.
When I showed my sons this website, I didn't tell them that the videos were math-related. I just opened up a video that I knew would interest them, "The Skateboard Designer," and asked them if they wanted to watch it. They started watching it, and one of them said, "Hey, mom! They use math for this!" They begged me to do the accompanying activity, but I wasn't able to get to it that day. They ended up watching several of the movies, and I had to pull them away from the computer so they wouldn't watch them all at once!
I am so excited to be finding such great sites that show the relevance of mathematics! Enjoy!