The NASA Visualization Explorer is a free app that allows you to explore a lot of the science NASA is doing on space-based Earth research. Topics covered include climate change, wildfires, glaciers, hurricanes, volcanoes and more. If it can be observed from an orbital platform, they will cover it sooner or later. This is a great way to get a comprehensive overview on how the planet is doing, and it is not just raw data dumps from the satellites. There are a lot of comprehensive yet concise presentations here, including narrated slide shows and full video presentations. They claim it is for the iPad only, but I am going to see if it will run on my iTouch; it looks like they have some data-dense screens you wouldn’t be able to read the text from but most of the presentations should play just fine on the small screen. You can grab it on iTunes.