Here’s a neat site with a collection of high-speed video clips. In addition to the usual water balloon and egg drops, Lucid Movement features some very extraordinary clips of things like balloons being popped underwater, or flint firestarters being filmed at 2000fps. This is a great resource for animators who want to see physical forces interact, or how certain chemical reactions happen, and it’s just plain interesting to watch tomatoes in a blender.
The owner of the site, Neil Nafus, also posts lots of information on the cameras he is using, and more interestingly, the special lighting setups that some of these subjects require. Also, you can purchase high-resolution footage of most of the clips, and there are several things that would make excellent backgrounds for motion graphics, like smoke or fire in super slow motion. You could probably also use things like these flames from an aerosol can for several special effects elements as well. My personal favorite is just simple water being blended.