Google Motion Graphs

This is an amazing gadget add on to Google Docs, which allows you to review 5 differnt data variables at once. Most useful is that it allows one of those variables to be time, so you can see how the data changes over time.
In the graph above, if you hit the play button you'll see 30 cities in China, with 3 highlighted - Shanghai, Beijing and Hangzhou. The vertical axis is time spent online each week and the horizontal axis it time spent watching TV yesterday. The size of the bubbles is population (of 15-24 year olds) and the colour is a warmth scale of how much newspapers they read.
When you hit play, you should see how over just 5 years, the time spent watching TV has fallen dramatically as the time online has increased. I've highlighted Hangzhou in particular where this is especially pronounced. The colour coding also highlights that these 15-24 year olds are reading less newspapers in 2009.
This is a great tool, you should try it.

Data from CHina Media and Marketing Survey 2004-2009