[throwaway946513]

I tinkered around with the idea of building an app that would get daily images from the space telescopes and the Mars rovers, as it turns out - NASA has an API dedicated to them (search for it, really easy to find via your favorite search engine).

I never ended up building anything from it quite yet (maybe soon), but the possibility is there, and the data is free to obtain. You have to register for an API key, but again, it's still free. The photos are updated quite frequently if I remember correctly.

Same thing can be said about the National Weather Service. You can get your weather forecasts in nice JSON formats from NOAA, all whilst not having to sell your data to The Weather Channel, or whatever alternatives exist for weather apps on Android.