NASA: iPad Visualisation Explorer (US only)

NASA has some of the coolest data around, of course. 

While you can dig around their numerous websites looking for gems, they have made life a lot easier for you and pulled together many of their best work into a free iPad App.

The quality of the visualisations is incredible, and most of them are well annotated/narrated. They add 8-10 new visualizations each month.

NB: Unfortunately, for now, the App is only available in the US but will be available in other areas later in the year.

NASA iPad Visualization Explorer