This is my first motion chart. It shows two tennis players, Federer and Ljubicic, and their change in rank and points earner over time. You can change the scale of the axes (linear or log), trace the players, color them differently, etc. This is my dad's data. My dad, Kresimir Adamic is into tennis and statistics. Matt Simmons, a student in my Fall '08 SI 601 class, demoed Google's motion chart gadget and I've been wanting to try it out ever since.
And if you haven't seen Hans Rosling's TED talk on using motion charts to show the relationship between health care, prosperity and birth rates, you're missing out.