Using area or volume to represent data can distort data values, and exaggerate differences between values. For example, if the radius of the circle is used to represent data values, the area of the circle will quadruple if the data values double. There is also an issue of 'perceptual scaling' - the tendency of people to underestimate areas.
How to create your own
Create your own: animation
Animations can be created in a range of standard data applications such as Excel, with the output saved for each different time-point, and an image editor or language such as Adobe Flash used to splice them into an animation. Online tools include Google Motion Charts.
Create your own: bubble chart
Bubble charts can be created in a range of standard data applications such as Excel.
Create your own: bubble map
Bubble maps can be created in a range of desktop GIS applications such as MapInfo and ArcGIS.