The 6 billion Others project by Yann Arthus-Bertrand:

In 2008 you will be able to listen to the thousands of testimonies which have been collected, and add your own testimony to the site.

Simple idea, neat & stylish execution, powerful impact. The system is built on Flash which works very well for the actual gallery of testimonies (unfortunately most of the rest of the site also runs on Flash which seems a little unnecessary, but this is a quibble). The back-story, about the inspiration for the project and a little about how it is being executed is also very interesting. Now, if only this was mashable.....

(Yann Arthus-Bertrand is the man behind the marvellous Earth from the Air project.)