Ciliates are protozoans that, despite being single cell critters, are surprisingly fast, large, and complex.
In part, because of that, they are probably one of the first thing people notice when looking at outdoor water under a microscope. The following video (taken with my microscope on my first weekend with it) captures a little bit of their speed, complexity, and size. (Click through on the video or here to see a larger version on YouTube)
The following, much more professionally developed video, captures the importance of ciliates to both education and research. (Side note: Carol Greider (from the video below) rode at the same stables that my wife keeps her horse),